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AN  INTRODUCTION 


TO 


NEUROLOGY 


BY 

C.  JUDSON  HERRICK 

PROFESSOR   OF   NEUROLOGY   IN    THE   UNIVERSITY    OF    CHICAGO 


SECOND  EDITION.  RESET 


PHILADELPHIA  AND  LONDON 

W.  B.  SAUNDERS  COMPANY 

1918 


Copyright,  igis,  by  W.   B.  Saunders  Company.     Reprinted  September,  igi6. 
Revised,  entirely  reset,  reprinted,  and  recopyrighted  October,  igi8 


Copyright,  1918,  by  W.  B.  Saunders  Company 


PRINTED     IN    AMERICA 

PRESS    OF 

W.    B.    SAUNDERS    COMPANY 

PHILADELPHIA 


PREFACE  TO  THE  SECOND  EDITION 


There  are  two  groups  of  functions  performed  by  the  nervous 
system  which  are  of  general  interest;  these  are,  first,  the  physio- 
logical adjustment  of  the  body  as  a  whole  to  its  environment 
and  the  correlation  of  the  activities  of  its  organs  among  them- 
selves, and,  in  the  second  place,  the  so-called  higher  functions 
of  the  cerebral  cortex  related  to  the  conscious  life.  The  second 
of  these  groups  of  functions  cannot  be  studied  apart  from  the 
first,  for  the  entire  conscious  experience  depends  for  its  mate- 
rials upon  the  content  of  sense,  that  is,  upon  the  sensory  data 
received  by  the  lower  brain  centers  and  transmitted  through 
them  to  the  cerebral  cortex.  Since  the  organization  of  these 
lower  centers  is  extremely  complex,  and  since  even  the  simplest 
nervous  processes  involve  the  interaction  and  cooperation  of 
several  of  these  mechanisms,  it  follows  that  an  understanding 
of  the  workings  of  any  part  of  the  nervous  system  requires  the 
mastery  of  a  large  amount  of  rather  intricate  anatomical  detail. 

Fortunately,  the  knowledge  of  the  precautions  which  must 
be  observed  in  order  to  maintain  the  nervous  system  in  healthy 
worldng  order  is  not  difficult  of  acquisition  (though  surpris- 
ingly few  people  seem  to  have  gained  it),  just  as  any  one  can 
learn  to  operate  an  automobile,  even  though  quite  ignorant  of 
the  engineering  problems  involved  in  its  design  and  construc- 
tion. Information  regarding  these  matters  of  practical  hy- 
giene is  readily  available,^  and  it  is  not  the  primary  purpose 
of  this  book  to  supply  it.  But  to  understand  the  actual  inner 
operation  of  the  nervous  mechanisms  is  a  much  more  difficult 
matter,  and  this  knowledge  cannot  be  acquired  without  ardu- 
ous and  sustained  study  of  the  peculiar  form  relations  of  the 
nervous  organs  and  their  complex  interconnections;  and  in- 
formation of  this  sort  is  indispensable  for  a  grasp  of  the  prin- 

^See  the  Bibliographj'  on  page  13. 
9 


10  PREFACE    TO    THE    SECOND    EDITION 

ciples  of  nervous  organization,  and  especially  for  an  intelligent 
treatment  of  nervous  diseases. 

The  study  of  neurology  is,  therefore,  intrinsically  difficult 
if  one  is  to  advance  beyond  its  most  superficial  phases ;  the 
more  so  if  the  student  is  not  well  grounded  in  general  biology 
and  at  least  the  elements  of  the  general  anatomical  structure 
of  the  vertebrate  body.  To  these  inherent  difficulties  there  is 
added  a  purely  artificial  obstacle  in  the  form  of  a  cumbersome 
and  confused  terminology  which  has  grown  up  during  several 
centuries  of  anatomical  study  of  the  brain,  in  the  early  stages 
of  which  little  or  no  comprehension  of  the  functional  signifi- 
cance of  the  parts  discovered  was  possible,  and  fanciful  or 
bizarre  names  were  given  without  reference  to  the  mutual 
relationship  of  parts. 

The  problems  which  at  present  chiefly  occupy  the  attention 
of  neurologists  are  of  three  sorts — first,  to  discover  the  regional 
localization  within  the  nervous  system  of  the  nerve-cells  and 
fibers  which  serve  particular  types  of  function  or,  briefly, 
architecture ;  second,  to  discover  the  chemical  or  other  changes 
which  take  place  during  the  process  of  nervous  function,  that 
is,  the  metabolism  of  the  nervous  tissues,  and  third,  how  to 
keep  the  nervous  system  in  health  and  to  diagnose  and  cure 
diseased  conditions.  The  first  of  these  problems  is  at  present 
further  advanced  than  the  second ;  the  larger  part  of  this  work 
is,  therefore,  devoted  to  a  description  of  architectural  relations. 
Without  a  knowledge  of  these  relations,  moreover,  the  problems 
of  function  cannot  be  approached.  The  medical  problems  of 
the  third  group  depend  upon  both  of  the  others;  with  these, 
however,  this  book  is  not  concerned. 

It  is  impossible  to  understand  clearly  the  form  of  the  brain, 
and  especially  the  relations  of  its  internal  structures,  from 
verbal  descriptions  merely.  Pictorial  illustrations  and  the 
various  brain  models  which  are  on  the  market  are  of  great 
assistance;  but  actual  laboratory  experience  in  dissecting  the 
brain  and,  if  possible,  the  study  of  microscopic  preparations 
of  selected  parts  of  it  are  indispensable  for  a  thorough  mastery 
of  the  subject.  The  brains  of  the  sheep,  dog,  and  cat  are 
easily  obtained,  and  are  so  similar  to  the  human  brain  in  all 
respects,  save  the  smaller  relative  size  of  the  cerebral  cortex, 


PREFACE    TO    THE    SECOND    EDITION  11 

that  they  can  readily  be  used  for  such  studies.  Before  dis- 
section the  brain  should  be  carefully  removed  from  the  skull 
and  hardened  by  immersion  for  a  few  days  in  a  solution  of 
formalin  (to  be  ol^tained  at  any  drug  store  and  diluted  with 
water  in  the  proportion  of  one  part  formalin  to  nine  parts 
water).  Several  neurological  laboratory  guides  have  been 
pubhshed,  and  one  of  these  should  be  followed  in  the  dissection.^ 

This  work  is  designed  as  an  introduction  in  a  literal  sense. 
Several  excellent  manuals  and  atlases  of  neurology  are  avail- 
able, and  to  these  the  reader  is  referred  for  the  illustrations  and 
more  detailed  descriptions  necessary  to  complete  the  rather 
schematic  outline  here  presented.  The  larger  medical  text- 
books of  anatomy  and  physiology  are,  however,  often  very 
difficult  for  the  beginner,  chiefly  on  account  of  the  lack  of  cor- 
relation of  the  structures  described  with  their  functions.  This 
little  book  has  been  prepared  in  the  hope  that  it  will  help  the 
student  to  learn  to  organize  his  knowledge  in  definite  func- 
tional patterns  earfier  in  his  work  than  is  often  the  case,  and 
to  appreciate  the  significance  of  the  nervous  system  as  a  work- 
ing mechanism  from  the  beginning  of  his  study. 

The  structure  and  functions  of  the  nervous  system  are  of 
interest  to  students  in  several  different  fields — medicine,  psy- 
chology, sociology,  education,  general  zoology,  comparative 
anatomy,  and  physiology,  among  others.  The  view-points 
and  special  requirements  of  these  various  groups  are,  of  course, 
different;  nevertheless  the  fundamental  principles  of  nervous 
structure  and  function  are  the  same,  no  matter  in  what  field 
the  principles  are  applied,  and  the  aim  here  has  been  to  pre- 
sent these  principles  rather  than  any  detailed  application  of 
them. 

In  the  selection  of  subject  matter  and  mode  of  treatment 
the  author  has  been  fortunate  in  having  the  advice  of  many 
experienced  teachers  in  several  fields,  who  have  read  the 
manuscript  of  this  work  or  of  selected  chapters  and  whose 
suggestions  have  contributed  greatly  to  its  value.  In  addition 
to  those  whose  names  are  mentioned  in  the  Preface  to  the 
First  Edition,  many  others  have  subsequently  offered  helpful 
criticisms.  The  list  of  these  names  would  be  too  long  for 
iSee  the  Bibliography  on  page  13. 


12  PREFACE    TO    THE    SECOND    EDITION 

publication  here  and  the  author  must  be  content  with   a 
general  acknowledgment  of  this  friendly  assistance. 

The  materials  presented  in  this  book  are  arranged  in  three 
groups:  (1)  Chapters  I  to  VII  discuss  the  more  general  neuro- 
logical topics;  (2)  Chapters  VIII  to  XVIII  comprise  a  brief 
account  of  the  form  of  the  nervous  system  and  the  functional 
significance  of  its  chief  subdivisions  in  general,  followed  by  a 
review  of  the  architectural  relations  of  the  more  important 
functional  systems;  (3)  Chapters  XIX  to  XXI  are  devoted  to 
the  cerebral  cortex  and  its  functions.  Readers  whose  chief 
interest  lies  in  the  general  neurological  questions  may  omit 
much  of  the  detail  comprised  within  the  second  group  of 
chapters  or  use  these  for  reference  only.  To  facilitate  ready 
reference  the  general  index  has  been  prepared  with  especial 
care,  and  with  it  is  combined  a  brief  glossary  of  some  more 
commonly  used  technical  terms.  In  the  text  some  of  the  more 
special  topics,  which  may  be  omitted  if  a  briefer  presentation 
is  desired,  are  printed  in  smaller  type. 

In  the  Second  Edition  there  has  been  no  departure  from 
the  original  plan  of  the  work,  but  it  has  been  thoroughly 
revised  and  somewhat  enlarged.  The  type  has  been  reset 
throughout  and  this  edition  is  printed  from  new  plates. 

C.  JuDSON  Herrick. 
Army  Medical  Museum,  Washington, 
October,  1918. 


GENERAL   NEUROLOGICAL    LITERATURE  13 

GENERAL  NEUROLOGICAL  LITERATURE 

The  following  references  include  titles  of  general  works 
and  books  of  reference  only.  For  literature  relating  to 
special  topics  consult  the  bibliographies  appended  to  the 
several  chapters.  All  citations  of  the  literature  given  in 
these  lists  are  entered  in  the  Index  under  the  authors'  names. 

Hygiene 

Carroll,  Robert  S.  1917.  The  Mastery  of  Nervousness, 
Based  upon  Self  Reeducation,  New  York. 

GuLicK,  Luther  H.     1907.     The  Efficient  Life,  New  York. 

Gulick,  Luther  H.     1908.     Mind  and  Work,  New  York. 

Jewett,  Francis  Gulick.  1898.  Control  of  Body  and 
Mind,  New  York,  Ginn  &  Co.  Adapted  for  use  in  the  graded 
schools. 

LuGARO,  E.  1909.  Modern  Problems  in  Psychiatry,  Man- 
chester University  Press.  A  book  written  especially  for  phy- 
sicians, but  full  of  stimulating  ideas  for  every  educated  reader. 

Stiles,  P.  G.  1917.  The  Nervous  System  and  Its  Con- 
servation, 2d  ed.,  Philadelphia,  W.  B.  Saunders  Company. 

Laboratory  Manuals 

Burkholder,  J.  F.  1912.  The  Anatomy  of  the  Brain, 
2d  ed.,  Chicago,  G.  P.  Engelhard  &  Co.  (Dissection  of  the 
brain  of  the  sheep.) 

FiSKE,  E.  W.  1913.  An  Elementary  Study  of  the  Brain 
Based  on  the  Dissection  of  the  Brain  of  the  Sheep,  New  York, 
The  Macmillan  Company. 

Hardesty,  I.  1902.  Neurological  Technique,  The  Uni- 
versity of  Chicago  Press.  (Dissection  of  the  human  brain  by 
means  of  transverse  gross  sections,  methods  of  microscopic 
preparation,  and  Hsts  of  neurological  terms.) 

Herrick,  C.  Judson,  and  Crosby,  Elizabeth.  1918.  A 
Laboratory  Outline  of  Neurology,  Philadelphia,  W.  B. 
Saunders  Co.  (Dissection  of  the  dogfish,  sheep,  and  human 
brains,  and  directions  for  study  of  prepared  microscopic 
sections  of  the  human  brain.) 


14  GENERAL   NEUROLOGICAL   LITERATURE 

Text-books  and  Atlases 

Barker,  L.  F.  1901.  The  Nervous  System  and  Its  Con- 
stituent Neurones,  New  York. 

Cunningham,  D.  J.  1915.  Text-book  of  Anatomy,  Re- 
vised 4th  ed.,  New  York. 

Flatau,  Ed.  1899.  Atlas  des  menschhchen  (jehirns  und 
des  Faserverlaufes,  Berhn. 

Van  Gehuchten,  A.  1906.  Systeme  Nerveux,  4th  ed., 
Louvain. 

Johnston,  J.  B.  1906.  The  Nervous  System  of  Verte- 
brates, Philadelphia. 

LuciANi,  L.     1915.     Human  Physiology,  London. 

Marbijrg,  0.  1904.  Atlas  des  Zentralnervensystems, 
Leipzig. 

Morris.     1914.     Human  Anatomy,  Part  III,  Philadelphia. 

Obersteiner,  H.  1912.  Anleitung  beim  Studium  des 
Baues  der  nervosen  Zentralorgane,  5th  ed.,  Leipzig. 

QuAiN.     1909.     Elements  of  Anatomy,  New  York. 

Ramon  y  Cajal,  S.  1909-1911.  Histologic  du  Systeme 
Nerveux,  Paris. 

Rauber  and  Kopsch.  1907.  Lehrbuch  der  Anatomie  des 
Menschen,  7th  ed.,  Abteilung  V,  Leipzig. 

Schaefer,  E.  a.     1900.     Physiology,  London. 

Sheldon,  R.  E.  1918.  The  Nervous  System,  New  York. 
(In  press.) 

Toldt,  Carl.  1904.  An  Atlas  of  Human  Anatomy,  Sec- 
tion VI,  London. 

Villiger,  E.     1912.     Brain  and  Spinal  Cord,  Philadelphia. 


CONTENTS 


PAGE 

Preface  to  the  Second  Edition 9 

General  Neurological  Literature 13 

CHAPTER   I 
Biological  Introduction 17 

CHAPTER   II 
The  Nervous  Functions 25 

CHAPTER   III 
The  Neubon 39 

CHAPTER   IV 

The  Reflex  Circuits 59 

CHAPTER   V 

The  Receptors  and  Effectors 74 

CHAPTER   \1 
The  General  Physiology  of  the  Nervous  System [102 

CHAPTER   VII 
The  General  Anatomy  and  vSubdivision  of  the  Nervous  System  114 

CHAPTER  VIII 
The  Spinal  Cord  and  Its  Nerves 136 

CHAPTER  IX 

The  Medulla  Oblongata  and  Cerebellum 155 

CHAPTER  X 

The  Cerebrum 175 

1.") 


16  CONTENTS 

CHAPTER   XI 

tAGE 

The  General  Somatic  Systems  of  Conduction  Paths 189 

CHAPTER  XII 

The  Vestibular  Apparatus  and  Cerebellum 201 

CHAPTER  XIII 

The  Auditory  Apparatus 217 


CHAPTER  XIV 


The  Visual  Apparatus. 


228 


CHAPTER  XV 

The  Olfactory  Apparatus 239 

CHAPTER  XVI 

The  Sympathetic  Nervous  System 249 

CHAPTER  XVII 

The  Visceral  and  Gustatory  Apparatus 261 

CHAPTER  XVIII 
Pain  and  Pleasure 277 

CHAPTER  XIX 
The  Structure  of  the  Cerebral  Cortex 292 

CHAPTER  XX 

The  Functions  of  the  Cerebral  Cortex 311 

CHAPTER  XXI 

The  Evolution  and  Significance  of  the  Cerebral  Cortex 335 

Index  and  Glossary 353 


INTRODUCTION  TO  NEUROLOGY 


CHAPTER     I 
BIOLOGICAL  INTRODUCTION 

The  living  body  is  a  little  world  set  in  the  midst  of  a  larger 
world.  It  leads  in  no  sense  an  independent  life,  but  its  con- 
tinued welfare  is  conditioned  upon  a  nicely  balanced  adjust- 
ment between  its  own  inner  activities  and  those  of  surrounding 
nature,  some  of  which  are  beneficial  and  some  harmful.  The 
great  problem  of  neurology  is  the  determination  of  the  exact 
part  which  the  nervous  system  plays  in  this  adjustment. 

This  problem  is  by  no  means  simple.  The  search  for  its 
solution  will  lead  us,  in  the  first  place,  back  to  an  examination 
of  some  of  the  fundamental  properties  of  the  simplest  living 
substance,  of  protoplasm  itself;  and  in  the  last  analysis  it  will 
involve  a  consideration  of  the  highest  mental  capacities  of  the 
human  race  and  of  the  physiological  apparatus  through  which 
these  capacities  come  to  expression.  We  shall  first  take  up  the 
nature  of  this  adjustment  on  the  lower  biological  levels. 

All  of  the  infinitely  diverse  forms  of  living  things  have  cer- 
tain points  in  common,  so  that  one  rarely  has  any  doubt 
.whether  a  given  object  is  alive  or  dead.  Nevertheless,  the 
precise  definition  of  life  itself  proves  very  difficult.  Herbert 
Spencer,  in  his  ''Principles  of  Biology,"  after  many  pages 
of  close  argument  and  rather  formidable  verbal  gymnastics, 
arrived  at  this  formula:  Life  is  "the  definite  combination  of 
heterogeneous  changes,  both  simultaneous  and  successive, 
in  correspondence  with  external  coexistences  and  sequences;" 
or,  more  briefly,  "The  continuous  adjustment  of  internal  re- 
lations to  external  relations."  A  somewhat  similar  idea  was 
subsequently  more  simply  expressed  by  the  late  C.  L.  Herrick 
2  17 


18  INTRODUCTION  TO  NEUROLOGY 

in  the  proposition.  ''Life  is  the  correlation  of  physical  forces 
for  the  conservation  of  the  individual;"  and  this,  in  turn,  may 
be  cast  in  the  more  general  form.  Life  is  a  system  of  forces 
maintained  by  a  continuous  interchange  of  energy  between  the 
system  and  its  environment,  these  forces  being  so  correlated 
as  to  conserve  the  identity  of  the  system  as  an  individual  and 
to  propagate  it.  A  certain  measure  of  modifiability  in  the 
character  of  the  system,  without  loss  of  its  individuality,  is  not 
excluded.  Child  has  recently  formulated  a  definition  of  life 
in  dynamic  terms  as  follows,  ''A  hving  organism  is  a  specific 
complex  of  dynamic  changes  occurring  in  a  specific  colloid 
substratum  which  is  itself  a  product  of  such  changes  and 
which  influences  their  course  and  character  and  is  altered 
by  them"  (Senescence  and  Rejuvenescence,  Chicago,  1915, 
p.  26). 

No  one  of  these  definitions,  or  any  other  which  has  been  sug- 
gested, is  fully  satisfactory;  but  biologists  generally  agree  that 
the  common  characteristics  of  living  beings  can  best  be  ex- 
pressed in  the  present  state  of  our  knowledge  in  terms  of  their 
actions,  their  behavior.  The  properties  commonly  ascribed 
to  any  object  are  in  last  analysis  names  for  its  behavior,  and 
the  so-called  vital  properties  are  very  special  forms  of  energy 
transformation. 

Now,  the  chief  difference  between  a  corpse  and  a  Uving  body 
consists  in  the  fact  that  the  forces  of  surrounding  nature  tend 
to  the  disintegration  of  the  dead  body,  while  in  the  living  body 
these  forces  are  utilized  for  its  upbuilding.  If,  then,  the  vital 
process  is  essentially  a  special  type  of  mutual  interaction  be- 
tween the  bodily  mechanism  and  the  forces  of  the  surrounding 
world,  of  the  correspondence  between  the  organism  and  the 
environment,  to  use  the  Spencerian  phrase,  it  follows  that  the 
living  body  cannot  be  studied  by  itself  alone.  Quite  the  con- 
trary, the  analysis  of  the  environmental  forces  upon  which  the 
life  of  the  body  depends  and  of  the  parts  of  the  body  itself 
in  their  relations  to  these  external  forces  is  the  very  kernel  of 
the  problem  of  life. 

The  measure  of  the  fulness  of  life  in  any  organism  is  two- 
fold. In  the  first  place,  the  life  is  measured  by  the  amount  of 
energy  which  the  organism  can  assimilate  from  surrounding 


BIOLOGICAL    INTRODUCTION  19 

nature  and  incorporate  into  its  own  organization.  This  enters 
the  body  chiefly  in  the  form  of  chemical  potential  energy  in' 
food  eaten,  air  breathed,  and  so  on,  and  can  be  quantitatively 
determined  and  stated  in  the  form  of  standard  units  of  energy-, 
such  as  calories  or  foot-pounds  of  work.  This  measures  the 
working  capacity  of  the  machine,  but  gives  little  insight  into 
the  real  value  of  the  work  done.  In  the  second  place,  life  may 
be  measured  in  terms  of  the  extensit}^  or  number  and  diversity 
of  environmental  relations.  This  takes  account  of  the  range 
or  working  distance  of  the  organization  and,  in  general,  of  the 
efficiency  of  the  work  done.  For  evidently  the  organism  which 
has  few  and  simple  relations  with  the  en^^ronment,  so  that  it 
can  adjust  itself  to  only  a  small  range  of  external  conditions, 
is  less  efficient  than  one  which  has  many  diverse  relationships 
and  an  extensive  series  of  possible  adjustments,  even  though 
the  actual  amount  of  energy  expended  may  be  vastly  greater  in 
the  former  than  in  the  latter  case.  The  first  of  these  standards 
is  a  tolerably  satisfactory  measure  of  the  vegetative  functions 
of  the  body,  sometimes  less  happily  termed  the  "organic 
functions."  We  have  no  word  in  common  use  which  covers 
precisely  the  group  of  activities  embraced  by  our  second 
standard  of  measurement,  though  the  terms  "animal  func- 
tions," "somatic  or  exteroceptive  activities"  are  sometimes 
used  in  about  this  sense. 

Let  us  now  endeavor  to  illustrate  the  last  topic  a  Httle  more 
concretely.  We  are  standing  on  a  hilltop  overlooking  a 
meadow,  through  which  runs  a  mountain  brook,  and  beyond 
the  valley  is  another  range  of  rugged  hills.  In  the  fence- 
corner  near  us  is  a  patch  of  daisies  and  clover  with  a  honey- 
bee buzzing  from  flower  to  flower.  A  plowboy  is  crossing 
the  field,  and  at  our  elbow  an  artistic  friend  is  busy  with  sketch- 
ing pad  and  brushes.  The  owner  of  the  farm  waves  a  greeting 
as  he  drives  past.  Here  are  five  things  which  have  this  at 
least  in  common,  that  they  are  alive — daisy,  bee,  plowboy, 
artist,  and  the  proprietor  of  the  estate.  There  can  be  no 
doubt  about  their  vitality,  but  how  differently  they  respond 
to  the  sunshine,  the  rain,  and  the  other  forces  of  nature. 

The  daisy  expands  in  the  vivifying  light  of  the  summer  sun, 
the  energy  of  whose  actinic  rays  is  used  to  build  up  hving 


20  INTRODUCTION  TO  NEUROLOGY 

protoplasm  and  vegetable  fiber  from  the  inert  substances  of 
air  and  soil.  Its  vitality,  measured  in  terms  of  energy  trans- 
formation, is  great;  yet  how  limited  its  range  of  life,  how  help- 
less in  the  face  of  the  storms  of  adversity  which  are  sure  to 
buffet  it.  Rooted  to  its  station,  it  can  only  assimilate  what 
food  is  brought  to  it  and  it  cannot  flee  from  scorching  wind  or 
blighting  frost. 

The  honey-bee  leads  a  more  free  and  varied  life.  Instead  of 
passively  and  blindly  waiting  for  such  bane  or  blessing  as  fate 
may  bring,  she  hurries  forth,  strong  of  wing  and  with  senses 
alert,  to  gather  the  daily  measure  of  honey  and  pollen.  The 
senses  of  touch,  sight,  and  smell  open  realms  of  nature  forever 
closed  to  the  plant,  and  enable  her  to  seek  food  in  new  fields 
when  the  local  supply  is  exhausted,  as  well  as  to  avoid  enemies 
and  misfortunes.  With  the  approach  of  the  storm,  she  fhes  to 
shelter  in  a  home  which  she  and  her  sisters  have  prepared  with 
consummate  skill.  Yet  in  this  provision  for  the  future  in  hive 
and  well-stocked  honeycomb  there  is  little  evidence  of  intelli- 
gent foresight  or  rational  understanding  of  the  purposes  for 
which  they  work.  Though  so  much  more  highly  organized  than 
the  plant,  the  honey-bee  is  to  a  very  large  extent  blindly  follow- 
ing out  the  inborn  impulses  of  her  hereditary  organization  and 
she  has  no  clear  understanding  of  what  she  does,  much  less  why 
she  does  it.  There  is  some  evidence  of  intelligent  adaptation 
in  her  behavior,  but  the  part  played  by  this  factor  in  her  life  as 
a  whole  is  probably  very  small  compared  with  the  blind  inborn 
impulses  which  dominate  most  of  her  activities.  Like  the 
plant,  the  bee's  reactions  are  determined  chiefly  by  the  past 
evolutionary  history  of  the  species,  which  has  shaped  the 
innate  organization  of  the  body  and  fixed  its  typical  modes  of 
response  to  stimulation.  But  the  bee  lives  much  more  in  the 
present  than  does  the  plant ;  that  is,  she  can  vary  her  behavior 
much  more  widely  in  response  to  the  needs  of  the  moment.  As 
for  the  future,  she  knows  naught  of  it. 

The  farmer's  boy  whistles  as  he  goes  about  his  work.  He, 
too,  has  a  certain  innate  endowment,  including  the  whole 
range  of  his  vegetative  functions,  together  with  an  instinctive 
love  of  sport  and  many  other  inborn  aptitudes.  This  is  his 
inheritance  from  the  past.     By  these  instincts  and  appetites 


BIOLOGICAL    INTRODUCTION  21 

he  is,  as  Dewey  says,  "pushed  from  behind"  through  the  per- 
formance of  many  bHndly  impulsive  acts.  He  is  a  creature  of 
the  present,  too,  his  whole  nature  overflowing  with  the  joy  of 
living.  But  he  also  looks  into  the  future  and  hastens  through 
the  daily  tasks  that  he  may  obtain  the  coveted  hour  of  sunset 
to  fish  in  the  brook.  He  flicks  off  the  heads  of  the  daisies  with 
his  whip-stock  and  remarks  in  passing,  "This  meadow  is 
choking  up  with  white- weed.  The  boss  will  have  to  plow  it 
up  next  year  and  replant  it."  The  extraordinary  natural 
beaut}^  of  the  place  is,  however,  unnoticed  amid  the  round  of 
daily  work  and  simple  pleasure. 

The  artist  looks  out  upon  the  same  scene,  but  through  what 
different  eyes!  The  mass  of  white  daisies  and  the  rocky  knoll 
beyond  ruddy  with  sheep  sorrel  suggest  to  him  no  waste  of 
valuable  pasture  land,  but  a  harmony  of  color  and  grace  of 
form  upon  which  he  feasts  his  soul.  The  esthetic  delights  of 
the  forest,  the  sky,  the  brook,  and  the  overhanging  crag  beyond 
are  for  him  unmixed  with  any  utilitarian  motive. 

Finally,  the  owner  turns  a  critical  eye  upon  his  meadow, 
appraising  it  as  part  of  an  entire  estate.  For  him  it  has  value 
as  a  commercial  asset  measured  in  terms  of  tons  of  hay  per 
acre,  as  an  esthetic  asset  measured  in  terms  of  appreciation 
of  scenic  beauty,  as  part  of  a  family  inheritance  to  be  con- 
served for  his  heirs,  and  as  a  responsibility  to  be  developed 
and  improved  as  a  social  obligation.  He  manifests  a  pride  of 
ownership  and  the  whole  face  of  nature  in  his  valley  is  changed 
to  conform  to  his  ideal. 

Each  of  these  five  organisms  occupies,  in  one  sense,  the 
same  environment;  but  it  is  evident  that  the  factors  of  this 
environment  with  which  each  comes  into  active  vital  relations 
are  immeasurably  different.  They  correspond  with  or  are  at- 
tuned to  quite  different  energy  complexes,  though  the  cor- 
respondence or  interaction  is  very  real  in  each  case.  This  has 
been  stated  very  simply  by  Dr.  Jennings  when  he  says  that 
every  species  of  organism  has  its  characteristic  "action  sys- 
tem," i.  e.,  a  habitual  mode  of  reaction  to  its  environment 
which  is  determined  wholly  or  in  part  by  its  inherited 
organization. 

Every  animal  and  every  plant  has,  accordingly,  a  definite 


22  INTRODUCTION  TO  NEUROLOGY 

series  of  characteristic  movements  which  it  can  make  in  re- 
sponse to  external  stimulation.  This  is  all  that  Jennings 
means  by  the  "action  system."  We  humans  are  no  exception 
to  this  rule  of  life.  We  move  along  in  a  more  or  less  stereo- 
typed way,  through  more  or  less  familiar  grooves,  in  our  daily 
work.  Much  of  this  work  is  routine,  done  about  as  mechani- 
cally as  the  flower  unfolds  its  petals  to  the  morning  sun  or  the 
honey-bee  gathers  in  her  store  of  honey.  This  is  our  action 
system.  Of  course,  we  have  much  else  to  do  besides  this 
routine,  and  our  actual  value  to  the  community  is  in  large 
measure  determined  by  our  ability  to  vary  this  routine  in 
adaptation  to  new  situations  as  they  arise.  Even  the  daisy  has 
a  little  of  this  capacity  for  independently  variable  action;  the 
insect  has  more;  and  man's  preeminence  in  the  world  is  due 
primarily  to  his  larger  powers  of  adapting  his  reactions  not 
only  to,  the  needs  of  the  moment,  but  to  probable  future  con- 
tingencies, i.  e.,  of  varying  his  inborn  action  system  by  in- 
telligently directed  choices. 

This  distinction  between  the  blind  working  of  a  stereotyped 
action  system  whose  character  is  determined  by  the  inherited 
bodily  structure,  on  the  one  hand,  and  individually  acquired 
variable  adaptive  actions  (which  may  or  may  not  be  intelli- 
gently performed),  on  the  other  hand,  is  very  fundamental, 
and  we  shall  have  occasion  to  return  to  it.  Most  animal  ac- 
tivities contain  both  of  these  factors,  and  it  is  often  very  dif- 
ficult to  analyze  a  given  example  of  behavior  into  its  elements, 
but  the  distinction  is  nevertheless  important.  Plant  life  is 
characterized  by  the  dominance  of  invariable  types  of  reaction' 
which  are  determined  by  innate  structure ;  these  in  their  most 
elementary  forms  give  us,  in  fact,  the  so-called  vegetative  func- 
tions. These  same  functions  predominate  in  the  lowest 
animals  also;  but  in  the  higher  animals,  as  we  shall  see,  there 
are  two  rather  distinct  lines  of  evolutionary  advance.  In  one 
line  the  innate  stereotyped  functions  are  very  highly  specia- 
lized, leading  up  to  a  complex  instinctive  mode  of  life;  in 
the  other  line  these  functions  are  subordinated  to  a  higher 
development  of  the  individually  acquired  variable  functions, 
leading  up  to  the  intelligence  and  docility  of  the  higher  mam- 
mals, including  the  human  race. 


BIOLOtaCAL    INTRODUCTION  23 

The  distinction  between  plants  and  animals  is  very  difficult 
to  draw  and,  in  fact,  there  are  numerous  groups  of  organisms 
which  at  the  present  time  occupy  an  ambiguous  position,  such 
as  the  slime  molds.  The  botanists  claim  them  and  call  them 
Myxomycetes;  the  zoologists  also  describe  them  under  the 
name  Mycetozoa;  still  other  naturalists  frankly  give  up  the 
problem  and  assign  them  to  an  intermediate  kingdom,  neither 
vegetable  nor  animal,  which  they  call  the  Protista.  As 
children  we  probably  considered  the  chief  distinction  between 
plants  and  animals  to  be  the  ability  of  the  latter  to  move  freely 
about;  but  one  of  the  first  lessons  in  our  elementary  biology 
was  the  correction  of  this  notion  by  the  study  of  sedentary 
animals  and  motile  plants.  Nevertheless,  I  fancy  that  in  the 
broad  view  the  childish  idea  has  the  root  of  the  matter  in  it. 
The  plants  and  sedentary  animals  may  have  their  vegetative 
functions  of  internal  adjustment  never  so  highly  specialized 
and  yet  remain  relatively  low  in  the  biological  scale  because 
their  relations  with  the  environment  are  necessarily  limited 
to  the  small  circle  within  which  they  first  take  root,  whereas 
the  power  of  locomotion  carries  with  it,  at  least  potentially, 
the  ability  to  choose  between  many  more  environmental 
factors.  It  is  only  the  free-moving  animals  that  have  any- 
thing to  gain  by  looking  ahead  in  the  world,  and  here  only  do 
we  find  well-developed  distance  receptors,  i.  e.,  sense  organs 
adapted  to  respond  to  impressions  from  objects  remote  from 
the  body.  And  the  distance  receptors,  as  we  shall  see,  have 
dominated  the  evolution  of  the  nervous  system  in  ver- 
tebrates and  determined  the  lines  it  should  follow. 

The  net  result  of  this  discussion  can  be  briefly  stated.  The 
differences  between  various  kinds  of  organisms  are,  in  the  main, 
incidental  to  the  extent  and  character  of  their  relations  with  the 
forces  of  surrounding  nature.  A  species  which  can  adjust  itself 
to  few  elements  of  its  environment  we  call  low;  one  that  can 
adapt  itself  to  a  wide  range  of  environmental  conditions  in  a 
great  variety  of  ways  we  call  higher.  The  supremacy  of  the 
human  race  is  directly  due  to  our  capacity  for  diversified  living. 
If  man  finds  himself  in  an  unfavorable  climate,  he  may  either 
move  to  a  more  congenial  locality  or  adapt  his  mode  of  life  by 
artificial  aids,  such  as  clothing,  houses,  and  fire.     And  in  these 


24  INTRODUCTION  TO  NEUROLOGY 

adaptations  he  is  not  limited  to  a  narrow  range  of  inherited 
instincts,  hke  the  hive  of  bees,  but  his  greater  powers  of  obser- 
vation and  reflection  enable  him  to  discover  the  general  uni- 
formities of  natural  process  (he  calls  these  laws  of  nature)  and 
thus  to  forecast  future  events  and  prepare  himself  for  them  in- 
telligently. In  other  words,  to  return  to  our  original  point  of 
view,  our  advantage  in  the  struggle  for  existence  lies  in  our 
ability  to  correlate  our  bodily  activities  with  a  wide  range  of 
natural  forces  so  as  to  make  use  of  these  forces  for  our  good 
rather  than  our  hurt.  (Of  course,  it  should  be  borne  in  mind 
that  this  formula  makes  no  pretense  of  being  an  exhaustive 
account  of  human  faculty;  but  only  that,  in  so  far  as  biological 
evolutionary  factors  have  operated  in  the  human  realm,  they 
act  in  accordance  with  this  principle.)  The  apparatus  by 
which  these  external  adjustments  are  effected  and  by  which  the 
inner  parts  of  the  body  are  kept  in  working  order  is  the  nervous 
system. 


CHAPTER  II 
THE  NERVOUS  FUNCTIONS 

The  body  is  composed  of  organs  and  tissues,  the  organs 
being  parts  with  particular  functions  to  perform  and  the  tis- 
sues being  the  cellular  fabric  of  wliich  the  organs  are  com- 
posed. The  tissues  (which  must  be  studied  microscopically) 
are  classified,  sometimes  in  accordance  with  the  general  func- 
tions which  they  serve,  such  as  the  nervous  and  muscular 
tissues,  and  sometimes  with  reference  to  the  forms  and  arrange- 
ments of  theii'  component  cells.  An  illustration  of  the  latter 
method  of  treatment  is  furnished  by  the  epithelial  tissues, 
which  are  thin  sheets  of  cells,  sometimes  arranged  in  one  layer 
(simple  epithelia),  sometimes  in  several  layers  (stratified 
epithelia).  Epithelial  tissues  may  perform  the  most  diverse 
functions. 

All  living  substance  (protoplasm)  possesses  in  some  measure 
the  distinctive  nervous  functions  of  sensitivity  and  conduc- 
tivity, that  is,  it  responds  in  a  characteristic  fashion  to  certain 
external  forces  (stimuH),  and  when  thus  stimulated  at  one 
point  the  movement  or  other  response  may  be  effected  by  some 
remote  part.  This  last  feature  impHes  that  some  form  of 
energy  is  conducted  from  the  site  of  the  stimulus  to  the  part 
moved.  Ordinary  protoplasm  also  possesses  the  power  of 
integration,  that  is,  of  combining  a  number  of  individual 
reactions  to  stimulation  in  diverse  special  adjustments. 

The  one-celled  animals  and  all  plants  lack  the  nervous  sj^s- 
tem  entirely;  nevertheless  they  are  able  to  make  highly 
complex  adjustments.  The  leaves,  roots,  and  stems  of  the 
higher  plants  have  individual  functions  which  are,  however, 
bound  together  or  integrated  into  a  very  perfect  unity.  In 
animals,  as  contrasted  with  plants,  we  see  a  further  differentia- 
tion of  parts  of  the  body  for  special  functions,  and  at  the  same 
time  a  more  perfect  correlation  of  part  with  part  and  integra- 

25 


26 


INTRODUCTION    TO    NEUROLOGY 


tion  of  the  whole  for  rapid  and  diversified  reactions  of  the 
entire  body.  The  nervous  system  is  the  apparatus  of  these 
more  perfect  adjustments  and  its  protoplasm  is  highly  modified 
in  different  directions.  Some  parts  may  be  especially  sensitive 
to  particular  forms  of  energy  (such  as  light  waves,  sound 
waves,  etc.,  this  being  termed  the  adequate  stimulus  in  each 
case);  other  parts,  the  nerves,  are  highly  modified  so  as  to 
conduct  nervous  impulses  from  part  to  part  with  a  minim]Lim 
expenditure  of  energy  and  loss  of  efficiency;  still  other  parts  of 
the  nervous  system  serve  as  centers  for  receiving  and  redis- 
tributing nervous  impulses  somewhat  after  the  fashion  of  the 


Fig.  1. — Diagram  illustrating  the  simplest  spinal  reflex  arc  consisting 
of  two  nervous  elements  or  neurons  (see  Chapter  III),  a  sensory  neuron 
connected  with  the  skin  and  a  motor  neuron  connected  with  a  muscle. 
Physiological  connection  between  the  two  neurons  is  effected  within  the 
spinal  cord.     (Modified  from  Van  Gehuchten.) 

central  exchange  of  an  automatic  telephone  system.  These 
are  the  correlation  centers,  and  they  are  larger  and  more 
complex  in  proportion  to  the  range  of  diversity  in  the  possible 
reactions  of  the  animal. 

The  simpler  reactions  to  stimulation  of  the  sort  here  under 
consideration  are  called  reflexes  (Fig.  1;  see  also  p.  59),  and  the 
essential  mechanism  is  a  reflex  arc  consisting  of  (1)  a  sensitive 
receiving  organ  (receptor  or  sense  organ);  (2)  a  conductor 
(afferent  or  sensory  nerve)  transmitting  the  nervous  impulse 
inward  from  the  receptor;  (3)  a  correlation  center  or  adjuster, 


THE    NERVOUS    FUNCTIONS  27 

generally  located  within  the  central  nervous  system;  (4)  a 
second  conductor  (efferent  or  motor  nerve)  transmitting  the 
nervous  impulse  outward  from  the  center  to  (5)  the  effector 
apparatus,  consisting  of  the  organs  of  response  (muscles, 
glands)  and  the  terminals  of  the  efferent  nerves  upon  them. 

No  part  of  the  nervous  system  has  any  significance  apart 
from  the  peripheral  receptor  and  effector  apparatus  with  which 
it  is  functionally  related.  This  is  true  not  only  of  the  nervous 
mechanism  of  all  physiological  functions,  but  even  of  the 
centers  concerned  with  the  highest  manifestations  of  thought 
and  feeling  of  which  we  are  capable,  for  the  most  abstract 
mental  processes  use  as  their  necessary  instruments  the  data  of 
sensory  experience  directly  or  indirectly,  and  in  many,  if  not 
all,  cases  are  intimately  bound  up  with  some  form  of  peripheral 
expression. 

The  neurologist's  problem  is  to  disentangle  the  inconceiv- 
ably complex  interrelations  of  the  nerve-fibers  which  serve  all 
the  manifold  functions  of  adjustment  of  internal  and  external 
relations;  to  trace  each  functional  system  of  fibers  from  its 
appropriate  receptive  apparatus  (sense  organ)  to  the  centers  of 
correlation;  to  analyze  the  innumerable  nervous  pathways  by 
which  these  centers  are  connected  with  each  other  (correlation 
tracts) ;  and,  finally,  to  trace  the  courses  taken  by  all  outgoing 
impulses  from  these  correlation  centers  to  the  peripheral 
organs  of  response  (muscles,  glands,  etc.,  or,  collectively,  the 
effectors). 

This  is  no  simple  task.  If  it  were  possible  to  find  an 
educated  man  who  knew  nothing  of  electricity  and  had  never 
heard  of  a  telegraph  or  telephone,  and  if  this  man  was  assigned 
the  duty  of  making  an  investigation  of  the  telegraph  and 
telephone  systems  of  a  great  city  without  any  outside  assist- 
ance whatever,  and  of  preparing  a  report  upon  all  the  physical 
equipment  with  detailed  maps  of  all  stations  and  circuits  and 
with  an  explanation  of  the  method  of  operation  of  every  part, 
his  task  would  be  simple  compared  with  the  problem  of  the 
neurologists.  The  human  cerebral  cortex  alone  contains  some 
9280  million  nerve-cells,  most  of  which  are  provided  with  long 
nerve-fibers  which  stretch  away  for  great  distances  and  branch 
in  different  directions,  thus  connecting  each  cell  with  many 


28  INTRODUCTION   TO   NEUROLOGY 

different  nerve-centers.     The  total  number  of  possible  nervous 
pathways  is,  therefore,  inconceivably  great. 

Fortunately  for  the  neurologists,  these  interconnecting  nerv- 
ous pathways  do  not  run  at  random;  but  just  as  the  wires 
entering  a  telephone  exchange  are  gathered  together  in  great 
cables  and  distributed  to  the  switchboards  in  accordance  with  a 
carefully  elaborated  system,  so  in  the  body  nerve-fibers  of  like 
function  tend  to  run  together  in  separate  nerves  or  within  the 
brain  in  separate  bundles  called  tracts.  Notwithstanding  the 
complexity  of  organization  of  the  nervous  organs,  the  larger 
and  more  important  functional  systems  of  nervous  pathways 
have  been  successfully  analyzed,  and  the  courses  of  nervous 
discharge  from  the  various  receptors  to  the  appropriate  centers 
of  adjustment,  and  from  these  (after  manifold  correlations  with 
other  systems)  to  the  organs  of  response,  are  fairly  well  known. 
The  acquisition  of  this  knowledge  has  required  several  cen- 
turies of  painstaking  anatomical  and  physiological  study, 
and  much  remains  yet  to  be  done. 

The  external  forms  of  the  brain  and  other  parts  of  the 
nervous  system  are  dependent  mainly  upon  the  arrangements 
of  the  nerve-cells  of  which  they  are  composed  (for  the  charac- 
teristics of  these  cells  see  Chapter  III),  and  these  arrange- 
ments, in  turn,  are  correlated  with  the  functions  to  be  per- 
formed. The  functional  connections  of  the  nerve-cells  can  be 
investigated  best  by  the  microscopical  study  of  the  tissues 
combined  with  physiological  experimentation.  From  this  it 
follows  that  the  study  of  the  gross  anatomy,  the  microscopical 
anatomy  (histology),  and  the  physiology  of  the  nervous  system 
should  go  hand  in  hand  so  far  as  this  is  practicable. 

A  study  of  the  comparative  anatomy  of  the  nervous  system 
shows  that  its  form  is  always  correlated  with  the  behavior  of 
the  animal  possessing  it.  The  simplest  form  of  nervous  system 
consists  of  a  diffuse  network  of  nerve-cells  and  connecting' 
fibers  distributed  among  the  other  tissues  of  the  body.  Such  a 
nervous  system  is  found  in  some  jelly-fishes  and  in  parts  of  the 
sympathetic  nervous  system  of  higher  animals.  Animals 
which  possess  this  diffuse  type  of  nervous  system  can  perform 
only  very  simple  acts,  chiefly  total  movements  of  the  whole 
body  or  general  movements  of  large  parts  of  it,  with  relatively 


THE    NERVOUS    FUNCTIONS 


29 


small  capacity  for  refined  activities  requiring  the  cooperation 
of  many  different  organs.  But  even  the  lowest  animals  which 
possess  nerves  show  a  tendency  for  the  nervous  net  to  be  con- 
densed in  some  regions  for  the  general  control  of  the  activities 
of  the  different  parts  of  the  body.  Thus  arose  the  central  nerv- 
ous system.  (Some  works  dealing  with  the  evolution  of  the 
nervous  system  are  cited  at  the  end  of  this  chapter.) 

The  aggregations  of  nervous  tissue  to  which  reference  has 
just  been  made,  containing  the  bodies  of  the  nerve-cells,  are 


Superior  ganglia 
Pharynx 
Inferior  ganglia 


\'entral  ganglia 


Fig.  2. — The  anterior  end  of  an  earthworm  (Lumbricus)  laid  open  from 
above  with  all  of  the  organs  dissected  away  except  the  ventral  body  wall 
and  ventral  ganglionic  chain. 


called  ganglia,^  and  in  all  invertebrate  animals  the  central 
nervous  system  is  a  series  of  such  ganglia,  variously  arranged  in 
the  body  and  connected  by  strands  containing  nerve-fibers 
only,  that  is,  by  nerves. 

The  central  nervous  systems  of  all  but  the  lowest  forms  of 
animals  are  developed  in  accordance  with  two  chief  structural 
patterns,  represented  in  typical  form  by  the  worms  and  insects 

^Ou  the  ganglia  of  the  vertebrate  nervous  system,  see  page  116. 


30  INTRODUCTION  TO  NEUROLOGY 

on  the  one  hand,  and  by  the  back-boned  animals  or  vertebrates 
on  the  other  hand. 

In  the  segmented  worms  (such  as  the  common  earthworm, 
Fig.  2)  the  central  nervous  system  consists  of  a  chain  of 
ganglia  connected  by  a  longitudinal  cord  along  the  lower  or 
ventral  wall  of  the  body.  Each  of  these  ganglia  is  connected 
by  mean^  of  peripheral  nerves  with  the  skin  and  muscles  of  its 
own  segment,  and  each  joint  of  the  body  with  its  contained 
ganglion  (ventral  ganglion)  has  a  certain  measure  of  physio- 
logical independence  so  that  it  can  act  as  a  unit.  This  is  a 
typical  segmented  nervous  system.  At  the  head  end  of  the 
body  the  ventral  ganglionic  chain  divides  around  the  pharynx 
and  mouth,  and  there  are  enlarged  gangha  above  and  below 
the  pharynx.  The  superior  ganglia  (supra-esophageal  ganglia) 
are  sometimes  called  the  brain,  and  this  organ  dominates 
the  local  activities  of  the  several  segments,  enabling  the 
animal  to  react  as  a  whole  to  external  influences. 

The  nervous  systems  of  crustaceans  (crabs  and  their  allies), 
spiders,  and  insects  have  been  derived  from  the  type  just 
described.  In  these  animals  the  segments  of  the  body  are 
more  or  less  united  in  three  groups,  constituting  respectively 
the  head,  thorax,  and  abdomen,  and  the  ganglia  of  the  central 
nervous  system  are  modified  in  a  characteristic  way  in  each 
of  these  regions.  Figure  3  illustrates  the  nervous  systems  of 
four  species  of  flies,  showing  different  degrees  of  concentration 
of  the  ganglia.  In  all  cases  the  head  part  (brain)  is  greatly 
enlarged,  and  is  arranged,  as  in  worms,  in  ganglia  above  and 
below  the  mouth  and  esophagus.  The  other  ganglia  are 
diversely  arranged,  from  the  simple  condition  (A)  where  there 
are  three  thoracic  gangha,  one  for  each  pair  of  legs,  and  six 
abdominal  ganglia,  through  intermediate  stages  {B  and  C), 
to  the  highest  form  (D),  where  all  of  the  ganglia  of  both  thorax 
and  abdomen  are  united  in  a  single  thoracic  mass. 

The  type  of  nervous  system  just  described  is  found  through- 
out the  highest  groups  of  invertebrate  animals,  as  in  insects 
and  spiders,  and  is  constructed  on  a  totally  different  plan  from 
that  of  all  of  the  vertebrate  or  back-boned  animals.  In  this 
latter  group  we  have,  instead  of  a  segmented  chain  of  ventrally 
placed  sohd  ganglia,  a  hollow  tube  of  nervous  tissue  which 


THE    NERVOUS    FUNCTIONS 


31 


extends  along  the  back  or  dorsal  wall  of  the  body  and  consti- 
tutes the  spinal  cord  and  brain.  The  cavit}-  or  lumen  of  this 
tube  extends  throughout  the  entire  length  of  the  central  nerv- 
ous system,  forming  the  ventricles  of  the  brain  and  the  cen- 
tral canal  of  the  spinal  cord.  The  details  of  the  invertebrate 
nervous  systems  (whose  structures  are  very  diverse)  will  not 
be  further  considered  in  this  work;  the  nervous  systems  of  all 
vertebrates,  however,  are  constructed  on  a  common  plan,  and, 


Fig.  3. — The  nervous  systems  of  four  species  of  flies,  to  illustrate  the 
various  degrees  of  concentration  of  the  ganglia:  A,  Chrionomus  plumosus, 
with  three  thoracic  and  six  abdominal  ganglia;  B,  Empis  stercorea,  with 
two  thoracic  and  five  abdominal  ganglia;  C,  Tabanus  bovinus,  with  one 
thoracic  ganglion  and  the  abdominal  ganglia  moved  toward  each  other;  D, 
Sarcophaga  carnaria,  with  all  thoracic  and  abdominal  ganglia  united  into 
a  single  mass.  (After  Brand,  from  Lang's  Text-book  of  Comparative 
Anatomy.) 

though  our  prime  interest  is  the  analysis  of  the  human  nerv- 
ous system,  we  shall  find  that  many  of  the  details  sought  can 
be  seen  much  more  clearly  in  the  lower  vertebrates  than  in 
man. 

Correlated  with  these  differences  between  the  structure  of 
invertebrate  and  vertebrate  nervous  systems  there  are  equally 
fundamental   differences  in   the   behavior   of  these   animals 


32  INTKODUCTION  TO  NEUROLOGY 

which  require  a  few  words  of  further  explanation.  Living 
substance  exhibits  as  its  most  fundamental  characteristic, 
as  we  saw  at  the  beginning,  the  capacity  of  adjusting  its 
own  activities  to  constantly  changing  environmental  condi- 
tions in  such  a  way  as  to  promote  its  own  welfare.  This 
adjustment  may  be  effected  in  two  ways,  both  of  which  are 
universally  present  and  which  throughout  the  remainder  of 
this  work  we  shall  call  the  invariable  or  innate  behavior  and  the 
variable  or  individually  modifiable  behavior. 

Every  animal  reaction,  then,  contains  these  two  factors,  the 
invariable  and  the  variable  or  individually  modifiable.  The 
first  factor  is  a  function  of  the  relatively  stable  organization  of 
the  particular  living  substance  involved.  The  pattern  of  this 
organization  is  inherited,  and  these  characteristics  of  the  be- 
havior are,  therefore,  common,  except  for  relatively  slight 
deviations,  to  all  members  of  the  race  or  species;  they  are 
rigidly  determined  by  innate  bodily  organization  so  arranged 
as  to  facilitate  the  appropriate  reactions,  in  an  invariable 
mechanical  fashion,  to  every  kind  of  stimulation  to  which  the 
organism  is  capable  of  responding  at  all.  In  the  strictly 
vegetative  functions,  in  all  true  reflexes  (as  these  are  defined  on 
page  59),  and  in  purely  instinctive  activities  in  general  this 
factor  of  behavior  is  dominant. 

But  in  addition  to  this  invariable  innate  behavior,  all  organ- 
isms have  some  power  to  modify  their  characteristic  action 
systems  in  adaptation  to  changed  environmental  relations. 
This  individual  modifiability  is  known  as  biological  regulation, 
a  process  which  has  of  late  been  very  carefully  studied.  We 
cannot  here  enter  into  the  problems  connected  with  form  regu- 
lation, that  is,  the  power  of  an  organism  to  restore  its  nor- 
mal form  after  mutilation  or  other  injury.  On  regulation  in 
behavior  reference  should  be  made  to  the  works  of  Jennings 
and  Child.  In  lower  organisms  Jennings  recognizes  three 
factors  in  the  regulation  of  behavior:  First,  the  occurrence  of 
definite  internal  processes;  these  form  part  of  the  invariable 
hereditary  action  system  referred  to  above.  Second,  inter- 
ference with  these  processes  causes  a  change  of  behavior  and 
varied  movements,  subjecting  the  organism  to  many  different 
conditions.     Third,  one  of  these  conditions  may  relieve  the 


THE    NERVOUS    FUNCTIONS  33 

interference  with  the  internal  processes,  so  that  the  changes 
in  behavior  cease  and  the  reheving  condition  is  thus  retained. 
Lack  of  oxygen,  for  instance,  would  interfere  with  an  animal's 
internal  processes;  this  leads  it  to  move  about;  if  finally  it 
enters  a  region  plentifully  supplied  with  oxygen,  the  internal 
processes  return  to  normal,  the  movement  ceases,  and  the 
animal  again  settles  down  to  rest.  If  this  regulatory  process 
is  oft  repeated  another  factor  enters,  viz.,  the  facilitation  of  a 
given  adjustment  by  repetition.  Thus  arise  physiological 
habits  or  acquired  automatisms. 

The  more  highly  complex  forms  of  individual  modifiability 
are  termed  associative  memory  and  intelligence,  and  the  latter 
of  these  is  by  definition  consciously  performed.  Whether 
consciousness  is  present  in  the  simpler  forms  of  "associative 
memory"  as  these  are  demonstrated  by  students  of  animal 
behavior  in  lower  animals  cannot  be  positively  determined. 
In  the  behavior  of  lower  animals  there  are  no  criteria  which 
enable  us  to  tell  whether  a  given  act  is  consciously  performed 
or  not,  and,  therefore,  the  lower  limits  of  intelligence  in  the 
animal  kingdom  are  problematical.  In  other  words,  the 
manifestations  of  variable  behavior  form  a  graded  series  from 
the  simple  regulatory  phenomena  of  unicellular  organisms, 
as  illustrated  above,  to  the  highest  human  intelligence,  so  far 
as  these  express  themselves  objectively. 

In  mankind,  where  intelligent  behavior  is  dominant,  the 
stereotyping  of  the  adjustments  by  repetition  (true  habit 
formation)  may  also  take  place,  and  in  this  case  the  acquired 
automatisms  are  sometimes  said  to  arise  by  "lapsed  intelli- 
gence," that  is,  an  act  which  has  been  consciously  learned  may 
ultimately  come  to  be  performed  mechanically  and  nearly  or 
quite  unconsciously.  Much  of  the  process  of  elementary 
education  is  concerned  with  the  establishment  of  such  ha- 
bitual reactions  to  frequently  recurring  situations.  How  far 
"lapsed  intelligence"  is  represented  in  the  so-called  instincts 
of  other  animals  is  still  a  debated  question  (see  p.  335). 

Among  the  invertebrate  animals,  the  insects  and  their  allies 
possess  a  bodily  organization  which  favors  the  performance  of 
relatively  few  movements  in  a  very  perfect  fashion,  that  is,  the 
action  system  is  simple  but  highly  perfected  within  its  own 

3 


34 


INTRODUCTION    TO    NEUROLOGY 


range.  Their  reflexes  and  instincts  are  very  perfectly  per- 
formed, but  the  number  of  such  reactions  which  the  animal 
can  make  is  rather  sharply  limited  and  fixed  by  the  inherited 
bodily  structure.  Their  behavior  is  dominated  by  the  invari- 
able and  innate  factors  and  they  cannot  readily  adapt  them- 
selves to  unusual  conditions.  The  vertebrates  likewise  have 
many  elements  of  their  behavior  which  are  similarly  fixed 


repTiles 


Vertebrate     Phylum 

Fig.  4. — Two  diagrams  illustrating  the  relative  development  of  the 
invariable  and  variable  factors  in  the  behavior  of  the  articulate  phylum 
and  the  vertebrate  phylum  of  the  animal  kingdom.  In  the  articulate 
phylum  the  invariable  factor  (represented  by  the  shaded  area)  predominates 
throughout;  in  the  vertebrate  phylum  the  invariable  factor  predominates 
in  the  lower  members  of  the  series,  and  the  variable  factor  (represented  by 
the  unshaded  area)  increases  more  rapidly  in  the  higher  members,  attaining 
its  maximum  in  man,  where  intelligence  assumes  the  dominant  r61e. 

or  stereotyped  in  their  innate  organization;  but,  in  addition 
to  these  stable  reflexes  and  instincts,  the  higher  members  of 
this  group  have  also  a  considerable  capacity  for  individual 
modifiability  in  behavior,  and  they  are  characterized  by  greater 
individual  plasticity  and  docility  (Yerkes).  It  appears  that 
the  tubular  type  of  nervous  system  found  in  vertebrates 
permits  of  the  development  of  certain  kinds  of  correlation 
mechanisms  which  are  impossible  in  the  more  compact  form 


THE    NERVOUS    FUNCTIONS  35 

of  ganglia  of  the  insects.  These  two  branches  of  the  animal 
kingdom  have,  therefore,  during  all  of  the  more  recent  evo- 
lutionary epochs  diverged  farther  from  each  other,  and  now, 
in  their  highl}'-  differentiated  conditions,  neither  type  could  be 
derived  from  the  other.  The  jointed  animals  (articulates)  de- 
veloped from  the  lower  worms,  and  this  branch  of  the  animal 
kingdom,  which  may  be  called  the  articulate  phylum,  cul- 
minates in  the  insects.  The  vertebrates  were  probably 
developed  from  similar  lowly  worm-like  forms  along  an  inde- 
pendent line  of  evolution,  and  this  branch  of  the  animal  king- 
dom, the  vertebrate  phylum,  cuminates  in  the  human  race. 
Figure  4  illustrates  in  a  rough  diagrammatic  way  the  relative 
development  of  the  variable  and  invariable  factors  of  be- 
havior in  the  articulate  and  vertebrate  phyla. 

In  unicellular  organisms  without  nervous  systems  the  gen- 
eral protoplasm,  of  course,  is  the  apparatus  of  both  the  invari- 
able and  the  variable  factors  of  behavior,  and  the  simpler 
forms  of  nervous  system  likewise  possess  both  of  these  ca- 
pacities. But  in  the  more  complex  forms  of  nervous  system 
among  vertebrates  special  correlation  centers  are  set  apart  for 
the  variable  activities,  particularly  those  which  are  intelH- 
gently  performed,  and  the  most  important  of  these  centers 
are  found  in  the  cerebral  cortex.  This  is  the  part  of  the  brain 
which  is  greatly  enlarged  in  mankind,  as  contrasted  with  all 
other  animals,  and  the  last  three  chapters  of  this  work  are 
devoted  to  the  structure  and  functions  of  these  cortical  mech- 
anisms with  whose  activity  the  progress  of  human  culture  is 
so  intimately  related. 

It  should  be  borne  in  mind  that  the  higher  correlation  centers 
which  serve  the  individually  variable  or  labile  behavior  in 
higher  vertebrates  can  act  only  through  the  agency  of  the 
lower  reflex  centers.  The  point  is,  that  all  of  the  elements 
of  behavior  are  represented  in  the  innate  neuro-muscular 
organization.  Every  single  act  which  the  animal  is  capable 
of  performing  has  its  mechanism  provided  in  the  inherited 
structure.  But  higher  animals  may  learn  by  experience  to 
combine  these  simple  elements  in  new  patterns.  The  higher 
correlation  centers  serve  this  function.  The  presence  and 
general  arrangement  of  these  centers  is,  of  course,  also  de- 


36  INTRODUCTION  TO  NEUROLOGY 

termined  in  heredity;  but  the  particular  associations  which 
will  be  effected  within  them  are  determined  by  individual 
experience,  and  the  building  up  of  these  new  associations  is 
the  chief  business  of  education  (see  p.  347).  In  the  analysis 
of  behavior  and  the  related  neurological  mechanisms  the 
distinction  between  the  innate  and  the  individually  acquired 
factors  must  always  be  kept  clearly  in  mind.  The  failure  to 
do  so,  and  also  the  failure  to  distinguish  between  these  two 
factors  and  the  acquired  automatisms  (p.  33),  is  responsible 
for  much  confusion  in  the  current  discussions  of  instinct. 

In  the  nomenclature  of  the  correlation  centers  there  is  considerable 
diversity  of  usage.  In  describing  the  adjustments  made  by  these  centers 
neurologists  frequently  use  the  words  coordination,  correlation,  and  asso- 
ciation in  about  the  same  sense;  but  the  adjustments  made  in  those  cen- 
ters which  lie  closer  to  the  receptors  or  sense  organs  are  physiologically 
of  different  type  from  those  made  in  the  centers  related  more  closely  to  the 
effector  apparatus.  In  recognition  of  this  fact  the  following  usage  has 
been  suggested  to  me  by  Dr.  F.  L.  Landacre  and  will  be  adopted  in  this 
work: 

The  term  correlation  is  applied  to  those  combinations  of  the  afferent 
impulses  within  the  sensory  centers  which  provide  for  the  integration  of 
these  impulses  into  appropriate  or  adaptive  responses;  in  other  words, 
the  correlation  centers  determine  what  the  reaction  to  a  given  combi- 
nation of  stimuli  will  be.  Nervous  impulses  from  different  receptors  act 
upon  the  correlation  centers,  and  the  reaction  which  follows  will  be  the 
resultant  of  the  interaction  of  all  of  the  afferent  impulses  (and  physiolog- 
ical traces  or  vestiges  of  previous  similar  responses)  involved  in  the  proc- 
ess. When  this  resultant  nervous  discharge  passes  over  into  the  motor 
centers  and  pathways,  the  final  common  paths  (pp.  62,  65)  innervated  will 
lead  to  a  response  whose  character  is  determined  by  the  organization  of 
the  particular  motor  centers  and  paths  actuated. 

To  the  term  coordination  we  shall  give  a  restricted  significance,  ap- 
plying it  only  to  those  processes  employing  anatomically  fixed  arrange- 
ments of  the  motor  apparatus  which  provide  for  the  co-working  of  par- 
ticular groups  of  muscles  (or  other  effectors)  for  the  performance  of 
definite  adaptively  useful  responses.  Every  reaction — even  the  simplest 
reflex — involves  the  combined  action  of  several  different  muscles,  and 
these  muscles  are  so  innervated  as  to  facilitate  their  concerted  action  in 
this  particular  movement.  These  are  called  synergic  muscles.  Coor- 
dination involves  those  adjustments  which  are  made  on  the  effector  side 
of  the  reflex  arc  (p.  59).  This  is  the  sense  in  which  the  term  is  applied 
by  Sherrington  in  the  following  passage  (Integrative  Action  of  the 
Nervous  System,  p.  84): 

"Reflex  coordination  makes  separate  muscles  whose  contractions  act 
harmoniously,  e.  g.,  on  a  lever,  contract  together,  although  at  separate 
places,  so  that  they  assist  toward  the  same  end.  In  other  words,  it 
excites  synergic  muscles.  But  it  in  many  cases  does  more  than  that. 
Where  two  muscles  would  antagonize  each  other's  action  the  reflex  arc, 
instead  of  activating  merely  one  of  the  two,  causes  when  it  activates  the 


THE    NERVOUS    FUNCTIONS  37 

one  depression  of  the  activity  (tpnic  or  rhythmic  contraction)  of  the  other. 
Tlie  latter  is  an  inhibitory  effect." 

The  motor  paths  and  centers  in  general  are  more  simply  organized  than 
are  the  sensory  paths  and  centers.  The  nervous  discharges  through  those 
motor  systems  are  very  direct  and  rapid.  Complex  nervous  reactions 
require  more  time  than  simple  reflexes,  and  this  delay  or  central  pause  is 
chiefly  in  the  correlation  centers  rather  than  in  the  efferent  coordination 
mechanisms  (see  pp.  71,  104,  198). 

The  word  association  may  be  reserved  for  those  higher  correlations 
where  plasticity  and  modifiability  are  the  dominant  features  of  the  re- 
sponse and  whose  centers  are  separated  from  the  peripheral  sensory  appa- 
ratus by  the  lower  correlation  centers  which  are  devoted  to  the  stereo- 
typed invariable  reflex  responses.  Correlation  may  be  mechanically 
determined  by  innate  structure,  or  there  may  be  some  small  measure  of 
individual  modifiability,  but  when  the  modifiability  comes  to  be  the 
dominant  characteristic,  so  that  the  result  of  the  stimulus  cannot  be  readily 
predicted  with  mechanical  precision,  the  process  may  be  called  associa- 
tion. The  intelligent  types  of  reaction  and  all  higher  rational  processes 
belong  here,  and  the  cerebral  cortex  is  the  chief  apparatus  employed. 

The  boundaries  between  the  three  types  of  centers  just  distinguished 
are  not  always  sharply  drawn,  especially  in  their  simpler  forms,  though  in 
general  they  are  easily  distinguished.  The  mechanisms  of  coordination 
are  neurologically  simpler  than  those  of  correlation  and  association,  and 
in  general  they  are  developed  in  the  more  ventral  parts  of  the  brain  and 
spinal  cord,  that  is,  below  the  limiting  sulcus  of  the  embryonic  brain  (p. 
129).  The  correlation  and  association  centers  are  developed  in  the  more 
dorsal  parts  of  the  brain  and  cord,  and  the  greater  part  of  the  thalamus 
and  cerebral  hemispheres  is  composed  of  tissue  of  this  type.  Neverthe- 
less, the  distinctions  here  drawn  are  fundamentally  physiological  rather 
than  anatomical,  and  coordination  centers  may  be  developed  in  the  dorsal 
parts  of  the  brain,  as  in  the  case  of  the  cerebellum  and  probably  also 
the  corpus  striatum  of  mammals  (though  not  the  striatum  of  lower 
vertebrates). 

Integration  is  the  combination  of  different  nervous  processes  or  re- 
flexes so  that  they  cooperate  in  a  larger  activity  and  thus  unify  the  bodily 
functions.  The  process  of  integration  is  the  highest  function  of  the 
nervous  system.  In  the  primitive  segmental  nervous  systems  (p.  30) 
each  segmental  ganglion  is  the  integrative  center  for  its  own  segment,  and 
the  fusion  of  ganglia  indicated  in  Figure  3  is  effected  in  the  interest  of 
more  complete  integration  of  the  activities  of  the  body  as  a  whole.  In 
the  evolution  of  the  vertebrate  type  of  nervous  system  there  has  been  a 
similar  progressive  condensation  of  centers  of  integration  in  the  brain. 
In  lower  vertebrates  the  isolated  spinal  cord  can  perform  many  functions 
which  in  man  require  the  participation  of  the  brain.  See  further  on  p. 
122. 

Summanj. — The  functions  which  characterize  the  nervous 
system  have  been  derived  from  those  of  ordinary  protoplasm 
by  further  development  of  three  of  the  fundamental  protoplas- 
mic properties — viz.,  sensitivity,  conductivity,  and  correla- 
tion. The  most  primitive  form  of  nervous  system  known  is 
diffuse  and  local  in  its  action,  but  in  all  the  more  highly  de- 


38  INTRODUCTION  TO  NEUROLOGY 

veloped  forms  the  chief  nervous  organs  tend  to  be  centrahzed 
for  ease  of  general  correlation  and  control.  Most  of  the  types  of 
nervous  systems  found  in  the  animal  kingdom  are  represented 
in  two  distinct  and  divergent  lines  of  evolution,  one  adapted 
especially  well  for  the  reflex  and  instinctive  mode  of  life  and 
found  in  the  worms,  insects,  and  their  allies,  and  the  other 
found  in  the  vertebrates  and  culminating  in  the  human  brain 
with  its  remarkable  capacity  for  individually  acquired  and 
conscious  functions. 

Literature 

Barker,  L.  F.  1901.  The  Nervous  System  and  Its  Constituent  Neu- 
rones, New  York. 

Child,  C.  M.  1911.  The  Regulatory  Processes  in  Organisms,  Journal 
of  Morphology,  vol.  xxii,  pp.  171-222. 

Edinger,  L.  1908.  The  Relations  of  Comparative  Anatomy  to 
Comparative  Psychology,  Jour.  Comp.  Neur.,  vol.  xviii,  pp.  437-457. 

Herrick,  C.  Judson.  1910.  The  Evolution  of  Intelligence  a;nd  Its 
Organs,  Science,  N.  S.,  vol.  xxxi,  pp.  7-18. 

— .  1910.  The  Relations  of  the  Central  and  Peripheral  Nervous 
Systems  in  Phylogeny,  Anat.  Record,  vol.  iv,  pp.  59-69. 

Jennings,  H.  S.  1905.  The  Method  of  Regulation  in  Behavior  and 
in  Other  Fields,  Jour.  Exp.  ZooL,  vol.  ii,  pp.  473-494. 

— .     1906.     Behavior  of  the  Lower  Organisms,  New  York. 

Lewandowsky,  M.  1907.  Die  Funktionen  des  zentralen  Nerven- 
systems,  Jena. 

LoEB,  J.  1900.  Comparative  Physiology  of  the  Brain  and  Com- 
parative Psychology,  New  York. 

Parker,  G.  H.  1909.  The  Origin  of  the  Nervous  System  and  Its 
Appropriation  of  Effectors,  Pop.  Sci.  Monthly,  vol.  Ixxv,  pp.  56-64,  137- 
146,  253-263,  338-345. 

— .  1914.  The  Origin  and  Evolution  of  the  Nervous  System,  Pop. 
Sci.  Monthly,  vol.  Ixxxiv,  pp.  118-127. 

Parmelee,  M.     1913.     The  Science  of  Human  Behavior,  New  York. 

Sherrington,  C.  S.  1906.  The  Integrative  Action  of  the  Nervous 
System,  New  York. 

Verworn,  M.     1899.     General  Physiology,  London. 

Washburn,  Margaret  F.     1908.     The  Animal  Mind,  New  York. 

Watson,  J.  B.  1914.  Behavior,  An  Introduction  to  Comparative 
Psychology,  New  York. 

Yerkes,  R.  M.  1905.  Concerning  the  Genetic  Relations  of  Types  of 
Action,  Jour.  Comp.  Neur.,  vol.  xv,  pp.  132-137. 


CHAPTER  III 

THE  NEURON 

As  we  have  seen  in  the  last  chapter,  the  functions  of  irrita- 
bihty,  conduction,  and  correlation  are  the  most  distinctive  fea- 
tures of  the  nervous  system.     Like  the  rest  of  the  body,  the 
nervous  tissues  are  composed  of  cells,  the  irritability  of  whose\ 
protoplasm  is  of  diverse  sorts  in  adaptation  to  different  func-\ 
tional  requirements.     Each  sense  organ,  for  instance,  is  irri-| 
table  to  its  own  adequate  stimulus  only  (see  pp.  26,  74).     The' 
functions  of  correlation  and  integration  of  bodily  actions  can- 
not be  carried  on  by  the  nerve-cells  as  individuals,  but  they  are 
effected  by  various  types  of  connections  between  the  different 
cells  in  the  nerve-centers.     The  character  of  any  particular 
correlation,  in  other  words,  is  a  function  of  the  pattern  in 
accordance  with  which  the  nerve-cells  concerned  are  connected 
with  each  other  and  with  the  end-organs  of  the  reflex  arcs 
involved.     The  conducting  function  of  nerve-cells  is,  perhaps, 
their  most  striking  peculiarity,  and  their  very  special  forms 
are  due  largely  to  the  fact  that  their  business  is  to  connect 
remote  parts  of  the  body  so  that  these  parts  can  cooperate 
in  complicated  movements. 

Not  all  of  the  cells  which  compose  the  central  nervous  system  are  nerve- 
cells.  In  addition  to  non-nervous  connective  tissue  elements  which  grow 
into  the  central  nervous  system  from  without  accompanying  the  blood- 
vessels, the  substance  of  the  brain  and  spinal  cord  contains  a  supporting 
framework  composed  of  ependyma,  neuroglia  fibers  and  glia  cells.  These 
are  not  known  to  perform  nervous  functions,  though  nutritive  and  other 
functions  have  been  ascribed  to  them  (see  p.  Ill  and  the  paper  by  Ach- 
ucarro  (1915). 

The  ependyma  is  the  membrane  which  lines  the  ventricles  of  the  brain 
and  spinal  cord.  It  is  derived  from  the  original  epithelium  of  the  em- 
bryonic neural  tube  (see  pp.  114,  125)  by  a  very  complicated  process  (see 
Hardesty,  1904).  This  primary  epithelium  also  gives  rise  to  free  cells 
which  lie  among  the  immature  ependyma  cells.  These  free  cells  are 
called  germinative  cells  or  indifferent  cells.  They  rapidly  increase  by 
division  and  some  of  them  ultimately  transform  into  the  nerve  cells, 
while  others  become  free  neuroglia  or  glia  cells.     From  the  neuroglia 

39 


40  INTRODUCTION  TO  NEUROLOGY 

cells  are  formed  numerous  tough  non-nervous  filaments,  the  neuroglia 
fibers,  which  interlace  to  form  a  felt-work  whose  function  seems  to  be 
merely  the  mechanical  support  of  the  brain  substance. 

The  true  nerve-cells  are  called  neurons.  There  has  been  a 
long  controversy  regarding  the  way  in  which  the  neurons  of 
the  adult  body  are  developed  from  the  cells  of  the  embryonic 
nervous  system;  but  it  is  now  generally  accepted  that  each 
neuron  is  developed  from  a  single  embryonic  cell  (known  as  a 
neuroblast),  and  that  in  the  adult  body  each  neuron  has  a 
certain  measure  of  anatomical  and  physiological  distinctness 
from  all  of  the  others. 

The  very  young  nerve-cell  (neuroblast)  is  oval  in  form  and  is 
composed  of  a  nucleus  and  its  surrounding  protoplasm  (cyto- 
plasm) ;  but  in  further  development  it  rapidly  elongates  by  the 
outgrowth  of  one  or  more  fibrous  processes  from  the  cell  body, 
so  that  the  mature  neuron  may  be  regarded  as  a  protoplasmic 
fiber  with  a  thickening  somewhere  in  its  course  which  is  the  cell 
body  of  the  original  neuroblast  and  contains  the  cell  nucleus 
and  a  part  only  of  its  cytoplasm  (this  part  being 'called  the 
perikaryon),  the  remainder  of  the  cytoplasm  composing  the 
fibrous  processes,  that  is,  the  nerve-fibers.  The  cell  body  of 
the  mature  neuron  is  sometimes  loosely  termed  the  nerve-cell, 
though  the  latter  term  should  strictly  include  the  entire  neu- 
ron. The  importance  of  the  conducting  function  is  reflected 
in  the  elongated  forms  of  the  neurons  and  in  the  peculiar 
protoplasmic  structure  of  the  nerve-fibers.  The  function  of 
the  cell  body  is  chiefly  nutritive;  the  entire  neuron  dies  if  the 
cell  body  is  destroyed. 

Each  neuron  may  be  regarded  as  essentially  an  elongated 
conductor,  and  these  units  are  arranged  in  chains  in  such  a 
way  that  a  nervous  impulse  is  passed  from  one  to  another  in 
series.  Since  the  arrangement  is  such  that  the  nervous  im- 
pulse usually  passes  through  the  series  in  only  one  direction 
(see  the  typical  reflex  arc.  Fig.  1,  p.  26),  each  neuron  has  a 
receptive  function  at  one  end  and  discharges  its  impulse  at 
the  other  end.  This  is  what  is  meant  by  the  polarity  of  the 
neuron  (see  pp.  55,    103). 

The  simpler  forms  of  neurons  are  bipolar,  with  one  or  more 
processes  known  as  dendrites  conducting  nervous  impulses 


THE    NEURONE 


41 


toward  the  cell  body,  and  (usually)  only  one  process,  the  axon 
or  neurite,  conducting  away  from  the  cell  body.     The  den- 


Fig.  5. — Diagram  of  a  motor  neuron  from  the  ventral  column  of  gray 
matter  in  the  spinal  cord.  The  cell  body,  dendrites,  axon,  collateral  branches, 
and  terminal  arborizations  in  muscle  are  all  seen  to  be  parts  of  a  single 
cell  and  together  constitute  the  neuron:  ah,  axon  hillock  free  from  chromo- 
philic  bodies;  ax,  axon;  c,  cytoplasm  of  cell  body  containing  chromophilic 
bodies,  neurofibrils,  and  other  constituents  of  protoplasm;  d,  dendrites; 
m,  myelin  (medullary)  sheath;  ??i',  striated  muscle-fiber;  n,  nucleus;  n', 
nucleolus;  nR,  node  of  Ranvier  where  the  axon  divides;  sf,  collateral  branch; 
si,  neurilemma  (not  a  part  of  the  neuron) ;  tel,  motor  end-plate.  (After 
Barker,  from  Bailey's  Histology.) 

drites  are  usually  short,  and  in  this  case  their  structure  is 
similar  to  that  of  the  cell  bod}^     But  where  the  dendrites 


42 


INTRODUCTION   TO    NEUROLOGY 


are  long,  as  in  the  neurons  of  the  spinal  and  cranial  ganglia 
(Figs.  1,  10),  they  may  have  the  same  structure  as  the  axon. 
The  axons  (and  in  the  case  of  neurons  of  the  spinal  and  cranial 
ganglia  the  dendrites  also)  are  the  axis-cylinders  of  the  longer 
nerve-fibers  and  are  structurally  very  different  from  the 
protoplasm  of  the  cell  body,  being  composed  chiefly  of  nu- 
merous very  delicate  longitudinally  arranged  neurofibrillse 
embedded  in  a  small  amount  of  more  fluid  protoplasm.     The 


Fig.  6. — Enlarged  view  of  a  cell  body  similar  to  that  of  Fig.  5,  from  the 
spinal  cord  of  an  ox,  showing  the  large  chromophilic  bodies:  a,  Pigment; 
h,  axon;  c,  axon  hillock;  d,  dendrites.     (After  von  Lenhossek.) 

axon  usually  arises  from  the  cell  body;  it  may  arise  from  the 
base  of  one  of  the  dendrites  or,  rarely,  from  the  apex  of  the 
chief  dendrite  (Fig.  11). 

The  forms  of  neurons  are  infinitely  diverse  and  appear  to 
have  been  determined  by  two  chief  factors;  these  are  (1) 
the  nutrition  of  the  cell  and  (2)  the  specific  functions  of  con- 
duction to  be  served.  The  dendrites  spread  widely  throughout 
the  surrounding  tissues,  thus  giving  the  cell  a  large  surface 
for  the  rapid  absorption  of  food  materials  from  the  surrounding 


THE    NEURON 


43 


lymph.  This  was  regarded  as  the  only  function  of  the  den- 
drites by  Golgi  and  some  of  the  other  pioneers  in  the  study 
of  neurons,  and  led  them  to  apply  the  name  "protoplasmic 
processes  "  to  these  structures.  We  have  alread}^  seen  that  the 
dendrites  are  more  than  this,  however,  being  the  usual  avenues 
by  which  nervous  impulses  enter  the  cell  body.  The  size, 
length,  and  mode  of  branching  of  the  dendrites  are,  therefore, 
chiefly  determined  by  their  relations  to  other  neurons  from 


Fig.  7. — The  body  of  a  pj-ramidal  neuron  from  the  cerebral  cortex,  stained 
by  Nissl's  method,  illustrating  the  arrangement  of  the  chromophilic  sub- 
stance and  the  form  of  the  nucleus:  a,  axon;  b,  chromophilic  bodies  sur- 
rounding the  nucleus;  c,  a  mass  of  chromophilic  substance  in  the  angle  formed 
by  the  branching  of  a  dendrite;  d,  nucleus  of  a  neuroglia  cell  (not  a  part  of 
the  neuron).     (After  Ramon  y  Cajal.) 

which  they  receive  their  nervous  impulses.  The  axon  prob- 
ably plays  but  little  part  in  the  general  nutrition  of  the  cell, 
and  its  form  is  shaped  almost  entirely  by  the  distance  to  be 
traversed  in  order  to  reach  the  center  or  centers  into  which 
it  discharges. 

Neurons  can  function  only  when  connected  together  in 
chains,  so  that  the  nervous  impulse  can  be  passed  from  one  to 
the  other.     In  any  such  chain  the  neuron  first  to  be  excited 


44  INTRODUCTION  TO  NEUROLOGY 

is  called  the  neuron  of  the  first  order,  and  the  succeeding 
members  of  the  series  neurons  of  the  second,  third,  fourth 
order,  and  so  forth.  All  reflexes  require  an  afferent  neuron 
which  conducts  the  nervous  impulse  from  the  receptor  to 
the  center,  one  or  more  efferent  neurons  conducting  from  the 
center  to  the  organ  of  response,  and  usually  one  or  more 
neurons  intercalated  between  these  within  the  center  itself 
(see  pp.  26,  59,  117).  Figure  1,  p.  26,  illustrates  the  simplest 
possible  connection  of  neurons  in  a  reflex  arc  of  the  spinal 
cord,  involving  only  two  elements.  The  afferent  neuron 
sends  its  dendrite  to  the  skin  and  its  axon  into  the  spinal  cord, 
where  the  nervous  impulse  is  taken  up  by  the  dendrites  of 
the  efferent  neuron,  which  in  turn  transmits  it  to  a  muscle. 
Figures  5  to  9  illustrate  the  forms  of  other  neurons. 

The  different  dendrites  of  a  neuron  may  be  physiologically 
all  alike,  or  they  may  spread  out  in  different  directions  to  receive 
nervous  impulses  of  diverse  sorts  from  different  sources. 
Similarly  the  axon  may  discharge  its  nervous  impulse  into  a 
,  single  nerve  center  or  peripheral  end-organ,  or  it  may  branch, 
thus  connecting  with  and  stimulating  to  activity  two  or  more 
diverse  functional  mechanisms.  In  other  words,  a  given 
neuron  may  be  a  link  in  a  chain  of  some  simple  nervous  circuit 
(Fig.  1),  or  it  may  be  adapted  to  collect  nervous  impulses 
from  different  sources  and  discharge  them  into  a  single  final 
common  path,  or  in  the  third  place  it  may  receive  nervous 
impulses  of  one  or  more  functional  sorts  and  then  discharge 
its  own  nervous  energy  into  several  remote  parts  of  the  nervous 
system.  This,  in  brief,  is  the  mechanism  of  correlation,  and 
illustrations  of  these  different  types  of  connection  will  be 
found  in  the  following  chapters.  If  animal  reactions  were 
simple  responses  so  arranged  that  a  given  stimulus  could 
produce  only  one  kind  of  movement,  the  only  nervous  mechan- 
ism required  would  be  a  single  neuron  transmitting  the  excita- 
tion from  the  point  of  stimulation  to  the  organ  of  response, 
as  a  call  bell  may  be  rung  by  pulling  a  bell  cord.  But  the 
actual  reactions  are  always  more  complex  than  this,  so  that 
several  neurons  must  be  connected  in  series  with  various  di- 
vergent pathways  of  nervous  discharge  which  reach  different 
correlation  centers,  all  of  which  must  cooperate  in  the  final 


THE    NEURON 


45 


response.     Illustrations  of  some  of  these  complicated  reflex 
mechanisms  will  be  found  in  Chapter  IV. 


Fig.  9. — Neuron  of  Type  II  from 
the  cerebral  cortex  of  a  cat.  The 
entire  neuron  is  included  in  the 
drawing:  a,  axon  which  branches 
freely  and  terminates  close  to  the 
cell  body;  d,  dendrites.  (After 
KoUiker.) 


Fig.  8. — Pyramidal  neuron  (Type 
1  of  Golgi)  from  the  cerebral  cortex 
of  a  rabbit.  The  axon  gives  off 
numerous  collateral  branches  close 
to  the  cell  body  and  then  enters  the 
white  substance,  within  which  it  ex- 
tends for  a  long  distance.  Only  a 
small  part  of  the  axon  is  included  in 
the  drawing:  a,  axon;  b,  white  sub- 
stance; c,  collateral  branches  of 
axon;  d,  chief  dendrite;  p,  its  ter- 
minal branches  at  the  outer  surface 
of  brain.     (After   Ramon  y   Cajal.) 

Neurons  with  short  dendrites  and  a  single  long  axon  are  the 
most  common  form  and  were  termed  Type  I  bj^  Golgi  (Fig.  8) . 


46  INTRODUCTION  TO  NEUROLOGY 

In  some  cases  (Fig.  9)  the  axon  also  is  very  short,  breaking  up 
in  the  immediate  neighborhood  of  the  cell  body;  these  are  the 
Type  II  neurons  of  Golgi  and  appear  to  be  adapted  for  the  diffu- 
sion and  summation  of  stimuli  within  a  nerve  center.  The 
neurons  of  the  spinal  and  cranial  ganglia  form  a  third  type. 
In  embryonic  development  they  begin  as  bipolar  cells  with  a 
dendritic  process  at  one  end  and  an  axonal  process  at  the 
opposite  end  of  the  cell  body;  but  in  the  course  of  further  devel- 
opment (Fig.  10)  the  two  processes  approach  each  other  and 
finally  unite  for  a  short  distance  into  a  single  stem,  which  then 
separates  into  an  axon  and  a  highly  special  form  of  dendrite 
which  has  the  same  microscopic  structure  as  the  axon,  but  con 


Fig.  10. — A  collection  of  cells  from  the  ganglion  of  the  trigeminus  of  the 
embryonic  guinea-pig,  to  illustrate  various  stages  in  the  transformation  of 
bipolar  neuroblasts  into  unipolar  ganglion  cells.     (After  Van  Gehuchten.) 

ducts  in  the  opposite  direction  with  reference  to  the  cell  body. 
This  produces  a  T-form  unipolar  cell. 

The  peculiarities  of  the  neurons  of  the  spinal  and  cranial  ganglia 
(Figs.  1  and  10)  have  given  rise  to  much  discussion.  Many  neurolo- 
gists consider  that  these  neurons  have  two  axons  and  no  dendrites  be- 
cause of  the  structural  similarity  of  their  two  chief  processes.  Dogiel, 
however,  has  described  many  different  types  of  neurons  in  the  spinal 
ganglia,  some  of  which  have  short  dendrites  of  the  more  typical  form. 
Lugaro  has  shown  that  the  neurons  of  the  spinal  gangUa  suffer  chromato- 
lysis  (see  p.  50)  when  the  peripheral  process  is  cut  off  from  the  cell  body 
but  not  when  the  central  process  is  similarly  severed.  This  has  also  been 
used  as  an  argument  against  regarding  the  peripheral  process  as  a  den- 
drite (see  A.  Meyer  in  Jour.  Comp.  Neurology,  vol.  viii,  1898,  pp.  265- 
267).  But  to  avoid  confusing  different  points  of  view,  it  seems  better  to 
define  dendrite  and  axon  in  terms  of  a  single  criterion,  viz.,  the  functional 
polarization  or  direction  of  conduction  with  reference  to  the  cell  body, 
as  on  page  40. 

Neurons  differ  in  internal  structure,  as  well  as  in  form,  from 
the  other  cells  of  the  body.     The  most  important  of  these  pecu- 


THE    NEURON  47 

liarities  are,  first,  the  fibrillar  structure  of  their  cytoplasm, 
and,  second,  the  presence  in  the  cytoplasm  of  a  highly  complex 
protein  substance  chemically  allied  to  the  chromatin,  which  is 
the  best  known  and  probably  the  most  important  constituent 
of  the  cell  nucleus.  This  is  the  chromophilic  substance,  which  in 
nerve-cells  as  seen  under  the  microscope  is  ordinarily  arranged 
in  more  or  less  definite  flake-like  masses  scattered  throughout 
the  cytoplasm  of  the  cell  and  extending  out  into  the  larger  den- 
drites (see  Figs.  6,  7).  These  masses  were  first  carefully  inves- 
tigated by  Nissl,  who  devised  a  special  staining  method  for  that 
purpose;  they  are,  accordingly,  often  called  the  Nissl  bodies, 


Fig.  11. — A  neuron  from  the  primary  gustatory  center  in  the  medulla 
oblongata  of  the  carp.  (Figure  139  (2),  p.  337,  illustrates  the  enormous 
enlargement  of  the  medulla  oblongata  of  this  fish  which  is  produced  by  this 
gustatory  center.)  The  peripheral  gustatory  nerves  end  among  the  den- 
drites, d.  The  axis  of  the  main  dendrite  is  directly  prolonged  to  form  the 
axon,  a.  The  heavy  line  at  the  right  marks  the  external  surface  of  the 
brain.     (From  the  Journal  of  Comparative  Neurology,  vol.  xv,  p.  395.) 

and  sometimes  tigroid  bodies.  They  never  occur  in  the  axon 
nor  in  a  special  conical  protuberance  of  the  cell  body  (the  axon 
hillock)  from  which  the  axon  arises  (see  Fig.  5,  ah,  and  Fig. 
6,  c). 

It  is  becoming  increasingly  probable  that  the  chromophilic 
substance  in  the  living  neuron  is  diffused  throughout  the 
protoplasm  and  that  the  definite  granules  (Nissl  bodies) 
seen  in  stained  preparations  are  fixation  artefacts  produced 
by  the  coagulation  of  this  substance  and  its  precipitation  by 
the  action  of  the  reagents  employed.  It  remains  true,  how- 
ever,  that  functionally  different  kinds  of  neurons  usually 


48 


INTRODUCTION   TO    NEUROLOGY 


exhibit,  when  fixed  and  stained  for  microscopic  study,  charac- 
teristic arrangements  of  the  chromophiHc  granules.  In  fact, 
the  Hmits  of  different  functional  centers  in  the  brain  can  often 


Fig.  12. — Cell  from  the  ventral  gray  column  of  the  human  spinal  cord, 
illustrating  the  arrangement  of  the  neurofibrils:  ax,  axon;  lu,  interfibrillar 
spaces  occupied  by  chromophilic  substance;  n,  nucleus;  x,  neurofibrils 
passing  from  one  dendrite  to  another;  y,  similar  neurofibrils  passing  through 
the  body  of  the  cell.     (After  Bethe,  from  Heidenhain's  Plasma  und  Zelle.) 

be  determined  by  this  criterion  alone,  that  is,  by  the  abun- 
dance, size,  and  arrangement  of  the  Nissl  bodies  as  contrasted 
with  the  neurons  of  surrounding  regions  with  different 
functions. 


THE    NEURON  49 

The  neurofibrils  are  very  delicate  strands  of  denser  proto- 
plasm found  in  all  parts  of  the  neuron  except  the  nucleus. 
They  are  by  many  regarded  as  the  specific  conducting  elements 
of  the  neuron,  though  the  evidence  for  this  is  not  conclusive. 
They  ramify  throughout  the  cytoplasm  (Fig.  12),  passing 
through  the  cell  body  from  one  process  to  another. 

Mitochondria. — Nerve-cells,  in  common  with  most  other  animal  and 
plant  cells,  possess  in  all  parts  of  their  protoplasm  except  the  nucleus 
very  small  granules  known  as  mitochondria  and  possessing  specific 
staining  properties.  Their  occurrence  in  nerve  cells  has  boen  carefully 
investigated  by  Cowdry.  Their  sizes  and  shapes  vary  in  different  kinds 
of  cells  and  in  the  same  cell  at  different  times.  These  granules  seem  to  be 
fundamental  ingredients  of  nearly  all  protoplasm  and  are  probal)ly  con- 
cerned in  the  most  fundamental  protoplasmic  activities.  Unlike  the  chro- 
mophilic  substance,  they  do  not  show  obvious  changes  when  the  nerve- 
cells  are  greatly  fatigued  and  their  precise  function  remains  obscure. 
Still  other  kinds  of  granules  are  known  to  occur  in  nerve-cells,  about  which 
our  knowledge  is  even  more  imperfect. 

The  longer  nerve-fibers  are  usually  enveloped  by  a  thick 
white  glistening  sheath  of  myehn,  a  fat-like  substance.  This 
myelin  sheath,  or  medullary  sheath,  is  usually  regarded  as 
a  part  of  the  neuron  with  which  it  is  related  and  the  fibers 
which  possess  it  are  called  myelinated  or  medulla  ted  fibers; 
these  fibers  compose  the  white  matter  of  the  brain  and  a  large 
part  of  the  peripheral  nerves  (see  Fig.  5).  There  maj^  be,  in 
addition,  in  the  case  of  the  peripheral  nerves  an  outer  sheath, 
the  neurilemma  (primitive  sheath  or  sheath  of  Schwann). 
This  is  a  thinner  nucleated  membrane,  not  a  part  of  the  neuron 
to  which  it  is  attached,  but  formed  from  surrounding  cells. 

Nemiloff  (1910)  describes  the  myehn  sheath  of  peripheral  nerves  as 
quite  separate  from  the  axis  cj^hnder,  but  on  the  other  hand  very  in- 
timately related  with  the  nuclei  of  the  neurilemma  sheath  of  the  ordinary 
descriptions.  But  these  nuclei  he  thinks  are  related,  not  to  the  neuri- 
lemma sheath,  but  to  a  spongy  protoplasmic  network  which  spreads 
throughout  the  myelin  sheath  and  has  heretofore  been  descrilied  as  the 
neurokeratin  network.  Neither  the  neurilemma  nor  the  myelin  sheath, 
on  this  view,  could  be  regarded  as  parts  of  the  neuron;  but,  with  the  con- 
tained protoplasmic  network  and  nuclei,  these  are  added  to  the  axis 
cylinder  from  the  surrounding  cells  during  the  development  of  the 
fiber.  This  description  applies  onh^  to  the  peripheral  nerves.  Nerves 
within'the  central  nervous  sj'stem  maj^  possess  myelin  sheaths  but  no  well- 
formed  neurilemma  or  nuclei.  It  is  therefore  difficult  to  understand  how 
Nemiloff's  description  can  apply  to  these  fibers,  and  this  matter 
evidently  requires  further  investigation. 
4 


50  INTRODUCTION  TO  NEUROLOGY 

The  function  of  the  myehn  sheath  has  often  been  regarded  as 
simply  that  of  an  insulating  substance  to  prevent  the  overflow 
and  loss  of  the  nervous  impulse  conducted  by  the  axon,  but 
there  is  some  evidence  that  this  sheath  plays  an  important  part 
in  the  chemical  processes  involved  in  the  act  of  nervous  conduc- 
tion. The  neurilemma  is  likewise  often  spoken  of  as  a  pro- 
tecting membrane.  Whether  it  has  any  other  function  in  the 
normal  life  of  the  nerve-fiber  is  unknown;  but  if  a  nerve-fiber 
is  by  accident  severed  from  its  cell  body,  it  is  known  that  the 
nuclei  of  the  neurilemma  play  a  very  important  part  in  the 
degeneration  and  regeneration  of  the  severed  fiber  and  the 
restoration  of  its  normal  function. 

As  has  been  suggested,  nerve-fibers  cut  off  from  their  cell 
bodies  immediately  die  and  degenerate.  But  in  the  case  of 
peripheral  nerves  the  neurilemma  nuclei  do  not  die;  and,  appa- 
rently with  the  aid  of  these  nuclei,  a  new  nerve-fiber  may  under 
favorable  conditions  grow  out  from  the  central  stump  of  the  cut 
nerve,  and  finally  the  entire  nerve  may  regenerate.  In  the  cen- 
tral nervous  system,  where  the  neurilemma  is  absent  or  greatly 
reduced,  the  regeneration  of  such  injured  nerves  takes  place 
with  great  difficulty,  if  at  all. 

It  is  possible  by  a  special  method  of  staining  devised  by 
Marchi  to  differentiate  myelinated  fibers  which  are  in  process 
of  degeneration  from  the  normal  fibers  with  which  they  may 
be  mingled.  This  method  has  often  permitted  a  much  more 
precise  determination  of  the  exact  course  of  the  fibers  of  a 
given  peripheral  nerve  or  central  tract  than  would  be  possible 
by  the  examination  of  normal  material,  especially  after  experi- 
mental operations  on  the  lower  animals,  where  the  particular 
collection  of  fibers  under  investigation  may  be  severed  and 
then  later  the  animal  killed  and  examined  by  Marchi's  method 
(see  p.  146). 

.  It  is  also  found  that  after  cutting  any  group  of  nerve-fibers 
the  cell  bodies  from  which  these  fibers  arise  show  structural 
changes.  The  most  important  change  is  a  solution  of  the 
chromophihc  substance  or  Nissl  bodies  so  that  they  no  longer 
appear  in  a  stained  preparation  (Fig.  13).  This  is  ternied 
chromatolysis,  and  often  enables  the  neurologist  to  determine 


THE    NEURON 


51 


exactly  which  cells  in  the  central  nervous  sytem  give  rise  to  a 
particular  bundle  of  fibers  (for  examples  see  pp.  148  and  316). 
The  neuron  doctrine  may  be  said  to  date  from  the  pubUca- 
tion  of  important  papers  by  Golgi,  of  Pa  via,  in  1882  to  1885 
(though  his  now  famous  method  was  published  in  1873,  and 
many  of  Golgi's  theoretical  conclusions  have  been  greatly 


Fig.  13. — Two  motor  neurons  from  the  ventral  column  of  gray  matter  of 
the  spinal  cord  of  a  rabbit,  taken  fifteen  days  after  cutting  the  sciatic  nerve, 
to  illustrate  the  chromatolysis  of  the  chromopliilic  substance:  A,  cell  in 
which  the  chromophilic  bodies  are  partially  disintegrated  (at  b)  and  the 
nucleus  eccentric;  B,  cell  showing  more  advanced  chromatolysis  (c),  the 
chromophilic  substance  being  present  only  in  the  dendrites  and  around  the 
nucleus  in  the  form  of  a  homogeneous  mass;  a,  axon.  Compare  with  these 
appearances  the  normal  cell  of  the  ventral  column  shown  in  Fig.  6.  (After 
Ramon  y  Cajal.) 

modified).  The  name  Neuron  (in  Enghsh  often  spelled 
"neurone")  was  first  applied  by  Waldeyer  in  1891  in  con- 
nection with  a  clear  enunciation  of  the  recently  demonstrated 
facts  upon  which  the  concept  is  based.  The  discovery  of 
William  His  that  the  nervous  system  is  made  up  of  cellular 
units   which   are   embryologically   distinct,   and   the   further 


52 


INTRODUCTION    TO    NEUROLOGY 


demonstration  by  others  that  these  cellular  elements  retain 
some  measure  of  anatomical  and  physiological  individuality 
(the  exact  degree  of  anatomical  separation  is  still  in  con- 
troversy— some  say  it  is  complete)  up  to  adult  life  revolu- 
tionized neurology,  and  this  doctrine  has  profoundly  influenced 
all  subsequent  neurological  work.     The  history  of  this  move- 


Fig.  14. — Neurons  from  the  trapezoid  body  of  the  medulla  oblongata  of  a 
cat,  illustrating  different  forms  of  synapse:  a,  Delicate  pericellular  net 
around  the  cell  body  of  a  neuron  which  is  not  shown;  h,  coarser  endings;  c, 
still  coarser  net;  d,  calyx-like  envelope.  In  b,  c,  and  d,  at  the  left  of  the 
figure,  the  globular  cell  body  of  the  neuron  of  the  second  order  is  shaded 
with  lighter  stipple  than  the  terminals  of  the  axon  of  the  neuron  of  the  first 
order.  (After  Veratti,  from  Edinger's  Vorlesungen.)  (It  should  be  noted 
that  in  this  account  we  do  not  follow  Veratti's  interpretations  of  these 
structures,  but  that  of  Held,  Ramon  y  Cajal,  and  the  majority  of  other 
neurologists.) 


ment  we  cannot  here  go  into  (see  the  excellent  summaries 
in  Barker's  Nervous  System  and  the  article  by  Adolf  Meyer 
cited  at  the  end  of  this  chapter).  The  present  status  of  the 
neuron  doctrine  has  been  summarized  by  Heidenhain  (1911, 
p.  711)  in  the  following  six  propositions: 

1.  The  neuron  of  the  adult  animal  body  is  an  anatomical 
unit;  it  corresponds  morphologically  to  one  cell. 


THE  NEURON 


53 


2.  The  neuron  is,  accordingly,  also  a  genetic  unit,  for  it  is 
differentiated  from  a  single  embryonic  cell. 

3.  Nervous  substance  is  composed  of  the  contained  neurons; 
within  the  nervous  system  there  are  no  elements  other  than 
neurons  which  participate  in  nervous  functions. 


Fig.  15. — Synapse  between  an  ascending  fiber  entering  the  cortex  of  the 
cerebellum  and  the  dendrites  of  a  Purkinje  cell.     (After  Ramon  y  Cajal.) 

4.  The  neurons  remain  anatomically  separate;  they  are 
merely  in  contact  with  each  other,  that  is,  there  are  no  con- 
nections between  them  which  are  characterized  as  conditions 
of  continuity  or  fusion  of  their  substance. 

5.  The  neuron  is  a  trophic  unit.  This  means  that  the  injury 
of  any  part  of  the  neuron  affects  the  welfare  of  the  whole,  and 
the  destruction  of  the  nucleus  and  cell  body  destroys  the  entire 
neuron,  but  such  injuries  do  not  directly  affect  adjacent 
neurons. 


54  INTRODUCTION  TO  NEUROLOGY 

6.  The  neuron  is  a  functional  unit  or,  better,  the  functional 
unit  of  the  nervous  system. 

These  six  propositions  are  accepted  in  their  entirety  by  many 
neurologists;  but  it  should  be  clearly  understood  that  all  of 
them  are  controverted  by  others.  The  fourth  proposition,  in 
particular,  has  been  the  subject  of  violent  attack  (see  the  dis- 
cussion of  the  synapse  below).  The  neuron,  moreover,  is  a 
functional  unit  (proposition  6)  in  only  a  rather  limited  sense 
(see  p.  59).  Without  further  discussion  of  the  merits  of  these 
controversial  questions,  it  may  be  regarded  as  generally  ac- 
cepted that  all  of  the  preceding  propositions  have  some 
measure  of  factual  basis,  though  different  neurologists  would 
give  various  interpretations  and  modifications  of  some  of  them. 


Fig.  16. — A  "basket  cell"  from  the  cerebellar  cortex  of  a  rat,  illustrating 
the  discharge  of  a  single  neuron,  5,  by  synaptic  connection  with  the  cell 
bodies  of  several  Purkinje  neurons.  A,  by  basket-like  endings  of  the  axon: 
A,  cells  of  Purkinje;  a,  the  basket-like  synapse  on  the  body  of  a  Purkinje 
cell;  B,  the  basket  cell;  b,  terminus  of  the  axon;  c,  axon  of  basket  cell.  (After 
Ram6n  y  Cajal;  cf.  Fig.  89,  p.  212.) 

The  place  where  the  axon  of  one  neuron  comes  into  physio- 
logical relation  with  another  neuron  is  known  as  the  synapse. 
Its  precise  nature  is  still  obscure.  Structurally  it  usually  ex- 
hibits a  dense  interlacing  of  the  terminal  arborization  of  an 
axon  of  one  neuron  with  the  bushy  dendrite  of  a  second 
neuron.  In  Fig.  1  (p.  26)  such  a  synapse  is  seen  between  the 
dorsal  root  neuron  and  the  ventral  root  neuron.  In  other  cases 
the  terminal  arborization  takes  the  form  of  a  delicate  network 


THE    NEUEON  55 

which  twines  around  the  cell  body  of  the  second  neuron  or  of  a 
calyx-like  expansion  or  coarse-meshed  reticulum  closely 
enveloping  the  cell  body  (Fig.  14).  Another  form  of  synapse 
is  seen  in  Fig.  15  from  the  cortex  of  the  cerebellum.  The  body 
and  larger  dendrites  of  a  single  cortical  neuron  of  the  type 
known  as  Pur  kin  je  cells  (see  p.  213)  are  shown  in  gray,  and  the 
terminal  branches  of  an  afferent  neuron  are  seen  twining  about 
the  dendritic  branches  of  the  Purkinje  cell,  thus  forming  a  very 
intimate  union.  Similar  synapses  are  found  in  the  cerebral 
cortex  (p.  301).  Figm-e  16  illustrates  a  type  of  synapse  also 
found  in  the  cerebellar  cortex.  A  single  "basket  cell,"  B,  has 
a  short  axon  whose  branches  form  synapses  around  the  bodies 
of  a  large  number  of  Pm'kinje  cells,  thus  diffusing  and  greatly 
strengthening  the  nervous  discharge  (see  p.  214  and  Fig.  89, 
h).  For  still  other  types  of  synapse  see  Figs.  61,  89,  98,  104, 
109,  126. 

The  synapse  has  been  a  crucial  point  in  recent  discussions 
regarding  the  general  physiology  of  the  nervous  system,  many 
neurologists  believing  that  it  is  the  most  important  part  of  the 
reflex  circuits  (see,  for  instance,  on  the  theory  of  sleep,  p.  110). 
The  doctrine  of  the  polarization  of  the  neuron  (p.  40)  impHes 
that  at  the  synapse  there  must  be  a  reversal  of  the  polarity 
with  reference  to  the  cell  body  as  the  nervous  impulse  passes 
over  from  an  axon  to  a  dendrite. 

In  the  simple  diffuse  form  of  nervous  system  found  in  primi- 
tive animals  like  the  jelly-fishes  and  lowest  worms  (p.  28)  the 
nerve-cells  are  described  as  connected  by  protoplasmic  strands 
to  form  a  continuous  network.  Here,  of  course,  there  are  no 
synapses  and  the  neurons  are  not  polarized.  Apparently  the 
nervous  impulse  may  be  transmitted  equally  well  in  all  direc- 
tions throughout  this  network.  The  physiological  properties 
of  such  an  arrangement  appear  to  be  very  different  from  those 
of  the  synaptic  nervous  systems  of  higher  animals.  A  non- 
synaptic  network  similar  to  that  mentioned  above  has  been 
described  as  occurring  in  some  of  the  diffuse  gangHonic  plex- 
uses of  the  human  body  (Fig.  17). 

In  the  synaptic  systems,  as  found  in  all  highly  differentiated 
nervous  centers,  the  majority  of  neurologists  teach  that  at  the 
synapse  the  two  neurons  involved  are  simply  in  contact  and 


56 


INTRODUCTION    TO    NEUROLOGY 


that  the  nervous  impulse  passes  from  one  to  the  other  across  a 
very  short  gap  in  the  conducting  substance.  Others  beheve 
that  they  have  demonstrated  very  dehcate  protoplasmic 
threads  which  bridge  this  gap,  thus  estabhshing  continuity  of 
the  conducting  substance  across  the  synapse.  Good  histolog- 
ical preparations  show,  however,  in  some  of  the  most  intimate 
synapses  known  where  the  axon  ends  directly  on  the  cell  body 


Fig.  17. — Plexus  of  sympathetic  neurons  in  the  villi  of  the  smaU  intes- 
tine of  a  guinea-pig:  a,  b,  c,  d,  Neurons  of  the  subepithelial  plexus;  e,  /, 
neurons  of  the  plexus  within  the  villi;  g,  fibers  of  the  submucous  (Meissner's) 
plexus.     (After  Ramon  yCajal.) 

of  the  second  neuron  that  there  is  a  distinct  cellular  membrane 
around  the  terminals  of  the  fibers  of  the  fii'st  order  and  a  second 
cellular  membrane  enveloping  the  body  of  the  neuron  of  the 
second  order,  so  that  continuity  of  the  ordinary  protoplasm  of 
the  neurons  here  seems  to  be  quite  impossible,  so  far  as  our 
present  technic  is  adequate  to  decide  the  question.^ 

1  For  an  illustration  of  such  a  synapse  see  Bartelmez,  G.  W., 
Mauthner's  Cell  and  the  Nucleus  Motorius  Tegmenti,  Jour.  Comp. 
Neur.,  vol.  xxv,  1915,  Figs.  11,  12,  and  13,  pp.  126-128. 


THK    NEURON  57 

The  following  important  points  regarding  the  synapse  seem 
to  be  established: 

1.  Unimpeded  protoplasmic  continuity  across  the  synapse 
has  not  been  clearly  established,  and  in  some  cases  there  is 
clearly  a  membranous  barrier  interposed  between  the  two 
neurons.  But  the  exact  nature  of  this  barrier  is  unknown  and 
it  by  no  means  follows  that  the  synaptic  membrane  is  an  inert 
substance.  It  ma}^  be  composed  of  living  substance  of  a  dif- 
ferent nature  from  that  of  the  other  protoplasm  of  the  neurons. 

2.  The  transmission  of  the  nervous  impulse  across  the  syn- 
apse involves  a  delay  greater  than  that  found  in  the  nerve-fiber 
or  the  cell  body.  This  suggests  that  there  is  some  sort  of  an 
obstruction  here  which  does  not  occur  elsewhere  in  the  reflex 
arc  (see  p.  104). 

3.  The  synapse  is  more  susceptible  to  certain  toxic  sub- 
stances, such  as  nicotin,  than  is  any  other  part  of  the  reflex  arc. 

4.  Though  a  nerve-fiber  seems  to  be  capable  of  transmitting 
an  impulse  in  either  direction,  the  nervous  impulse  can  pass  the 
synapse  in  only  one  direction,  viz.,  the  direction  of  normal  dis- 
charge from  the  axon  of  one  neuron  to  the  dendrite  of  another. 
The  synapse,  therefore,  acts  as  a  sort  of  valve,  to  use  a  crude 
analogy,  and  appears  to  be  one  of  the  factors  (not  necessarily 
the  only  one,  see  p.  103)  in  estabhshing  the  polarity  of  the 
neuron. . 

5.  Observations  upon  injured  neurons  show  that  the  degen- 
erations caused  by  the  severance  of  their  fibrous  processes 
(whether  these  be  manifested  as  degeneration  of  the  fibers  or  as  ■ 
chromatolj^sis,  see  p.  50)  or  by  the  destruction  of  the  cell  bodies 
from  which  the  fibers  arise  cannot  cross  the  barriers  interposed 
by  the  sjmapses. 

Summary. — In  this  chapter  the  form  and  internal  structure 
of  neurons  have  been  briefly  reviewed  and  the  present  status  of 
the  neuron  doctrine  is  summarized  on  p.  52.  The  sj'^napse  is 
the  place  where  the  nervous  impulse  is  transmitted  from  one 
neuron  to  another,  and  it  is  regarded  as  of  the  utmost  physio- 
logical importance,  its  most  important  features  being  presented 
briefly  on  this  page,  above.  The  doctrine  of  the  polarization 
of  the  neuron  teaches  that  nervous  impulses  are  received  by 


58  INTRODUCTION   TO    NEUROLOGY 

the  dendritic  processes  and  transmitted  outward  from  the  cell 
body  through  the  axon. 

Literature 

ACHTJCARRO,  N,  1915.  De  revolution  de  la  nevroglie  et  specialement 
de  ses  relations  avec  I'appareil  vasculaire,  Trav.  du  Lab.  Biol,  de  Madrid, 
vol.  xiii. 

Apathy,  S.  1898.  Ueber  Neurofibrillen,  Proc.  Internat.  Zoological 
Congress,  Cambridge,  pp.  125-141. 

Barker,  L.  F.  1901.  The  Nervous  System  and  Its  Constituent  Neu- 
rones, New  York. 

Bethe,  a.  1904.  Der  heutige  Stand  der  Neurontheorie,  Deutsch. 
med.  Woch.,  No.  33. 

CowDRY,  E.  V.  1912.  The  Relations  of  Mitochondria  and  other  Cy- 
toplasmic Constituents  in  Spinal  Ganglion  Cells  of  the  Pigeon,  Intern. 
Monatsschrift  f.  Anat.  u.  Physiol.,  Bd.  xxix. 

— .  1914.  The  Development  of  the  Cytoplasmic  Constituents  of 
the  Nerve-cells  of  the  Chick,  Am.  Jour.  Anat.,  vol.  xv,  pp.  389-429. 

DoGiEL,  A.  S.  1908.  Der  Bau  der  Spinalganglien  des  Menschen  und 
der  Saugetiere,  Jena. 

GoLGi,  C.  1882-1885.  Sulla  fina  anatomia  degli  organi  centrali  del 
sistema  nervosa,  Riv.  Sperim.  di  Freniatria,  vols,  viii,  ix,  and  xi. 

— .  1907.  La  dottrina  del  neurone,  Teoria  e  fatti.  Arch.  Fisiol., 
vol.  iv,  pp.  187-215. 

Hardesty,  I.  1904.  On  the  Development  and  Nature  of  the  Neu- 
roglia, Am.  Jour.  Anat.,  vol.  iii,  pp.  229-268. 

Heidenhain,  M.  1911.  Plasma  und  Zelle,  2  Lieferung  (in  Bardele- 
ben's  Handbuch  der  Anatomie  des  Menschen,  Bd.  8),  Jena. 

His,  W.  1889.  Die  Neuroblasten  und  deren  Entstehung  im  embry- 
onalen  Mark,  Leipzig. 

Meyer,  Adolf.  1898.  Critical  Review  of  the  Data  and  General 
Methods  and  Deductions  of  Modern  Neurology,  Jour.  Comp.  Neur., 
vol.  viii,  pp.  113-148  and  249-313. 

Nemiloff,  a.  1910.  Ueber  die  Beziehung  der  sog.  "Zellen  der 
Schwannschen  Scheide  "  zum  Myelin  in  der  Nervenf asern  von  Saugetiere, 
Arch.  f.  mikr.  Anat.,  Bd.  76,  pp.  329-348. 

NissL,  F.     1903.     Die  Neuronenlehre  und  ihre  Anhanger,  Jena. 

Ramon  y  Cajal,  S.     1909.     Histologie  du  Systeme  Nerveux,  Paris. 

Strongman,  B.  T.  1917.  A  Preliminary  Experimental  Study  on  the 
Relation  between  Mitochondria  and  the  Discharge  of  Nervous  Activity, 
Anat.  Record,  vol.  xii,  pp.  167-171. 

Waldeyer,  W.  1891.  Ueber  einige  neuere  Forschungen  im  Ge- 
biete  der  Anatomie  des  Centralnervensystems,  Deutsch.  med.  Woch., 
Bd.  17. 


CHAPTER  IV 

THE  REFLEX  CIRCUITS 

The  cellular  unit  of  the  nervous  system,  as  we  have  seen,  is 
the  neuron.  Neurons,  however,  never  function  independently, 
but  only  when  joined  together  in  chains  whose  connections  are 
correlated  with  the  functions  which  they  serve.  Accordingly, 
the  most  important  unit  of  the  nervous  system,  from  the  physi- 
ological standpoint,  is  not  the  neuron,  but  the  reflex  circuit,  a 
chain  of  neurons  consisting  of  a  receptor  or  sensory  organ,  a 
correlating  center  or  adjustor,  and  an  effector  or  organ  of 
response,  together  with  afferent  and  efferent  nerve-fibers  which 
serve  as  conductors  between  the  center  and  the  receptor  and 
effector  respectively  (see  p.  26),  In  a  reflex  circuit  the  parts 
must  be  so  connected  that  upon  stimulation  of  the  receptive 
end-organ  a  useful  or  adaptive  response  follows,  such,  for  in- 
stance, as  the  immediate  jerking  away  of  the  hand  upon 
accidentally  touching  a  hot  stove. 

A  reflex  act,  as  this  term  is  usually  defined  by  the  physiolo- 
gists, is  an  invariable  mechanically  determined  adaptive  re- 
sponse to  the  stimulation  of  a  sense  organ,  involving  the  use  of 
a  center  of  correlation  and  the  conductors  necessary  to  connect 
this  center  with  the  appropriate  receptor  and  effector  appa- 
ratus. The  act  is  not  voluntarily  performed,  though  one  may 
become  aware  of  the  reaction  during  or  after  its  performance. 

The  term  ''reflex"  is  often  popularly  ver}'^  loosely  applied, 
but  as  generally  used  by  physiologists  it  involves  the  rather 
complex  nervous  function  above  described.  If  an  electric 
shock  is  applied  directly  to  a  muscle  or  to  the  motor  nerve 
which  innervates  that  muscle,  the  muscle  will  contract,  but 
this  direct  contraction  is  not  a  reflex  act.  Many  acquired 
movements  have  become  so  habitual  as  to  be  performed  quite 
automatically,  such  as  the  play  of  the  fingers  of  an  expert 
pianist  or  typist;  but  these  acquired  automatisms  must  be 

59 


go  INTRODUCTION  TO  NEUROLOGY 

clearly  distinguished  from  the  reflexes,  which  belong  to  the  in- 
nate nervous  organization  with  which  we  are  endowed  at  birth 
(see  pp.  33,  335).  The  lowly  organisms  which  lack  a  differen- 
tiated nervous  system  exhibit  many  kinds  of  behavior  which 
closely  resemble  reflexes  and,  in  fact,  are  physiologically  of  the 
same  type;  but  these  non-nervous  responses  are  usually  termed 
tropisms  or  taxes,  though  some  physiologists  call  them  reflexes, 
and  some  reflexes,  as  above  defined,  are  often  called  tropisms. 

The  structure  of  the  simple  reflex  circuit  is  diagrammatically 
illustrated  in  Fig.  18,  A.  The  receptor  (R)  may  be  a  simple 
terminal  expansion  of  the  sensory  nerve-fiber  or  a  very  complex 
sense  organ.  The  effector  {E)  may  be  a  muscle  or  a  gland. 
The  cell  body  of  the  afferent  neuron  (1)  may  lie  within  the  cen- 
ter (C)  or  outside,  as  in  the  diagram.  The  latter  condition  is 
more  usual,  as  seen  in  the  spinal  and  cranial  ganglia  (Fig.  1,  p. 
26).  The  synapse  and  the  cell  body  of  the  efferent  neuron  (2) 
lie  in  the  center. 

A  simple  reflex  act  involving  the  use  of  so  elementary  a  mech- 
anism as  has  just  been  described  is  probably  never  performed 
by  any  adult  vertebrate.  The  nervous  impulse  somewhere  in 
its  course  always  comes  into  relation  with  other  reflex  paths, 
and  in  this  way  complications  in  the  response  are  introduced. 
Some  illustrations  of  the  simpler  types  of  such  complex  reflex 
circuits  will  next  be  considered. 

Separate  reflex  circuits  may  be  so  compounded  as  to  give  the 
so-called  chain  reflex  (Fig.  18,  B).  Here  the  response  of  the 
first  reflex  serves  as  the  stimulus  for  the  second,  and  so  on  in 
series.  The  units  of  these  chain  reflexes  are  usually  not  simple 
reflexes  as  diagrammed,  but  complex  elements  of  the  types  next 
to  be  described. 

Figure  18,  C  illustrates  another  method  of  compounding  re- 
flexes so  that  the  stimulation  of  a  single  sense  organ  may  excite 
either  or  both  of  two  responses.  If  the  two  effectors.  El  and 
E2,  can  cooperate  in  the  performance  of  an  adaptive  response, 
the  case  is  similar  to  that  of  Fig.  18,  A,  with  the  possibility  of  a 
more  complex  type  of  reaction.  This  is  an  allied  reflex.  If, 
however,  the  two  effectors  produce  antagonistic  movements,  so 
that  both  cannot  act  at  the  same  time,  the  result  is  a  physio- 
logical dilemma.     Either  no  reaction  at  all  results,  or  there  is  a 


THE    REFLEX    CIRCUITS 


61 


sort  of  physiological  resolution  (sometimes  called  physiological 
choice),  one  motor  pathway  being  taken  to  the  exclusion  of  the 
other.  Which  path  will  be  chosen  in  a  given  case  may  be 
determined  by  the  physiological  state  of  the  organs.     If,  for 


Fig.  18. — Diagrams  representing  the  relations  of  neurons  in  five  types  of 
reflex  arcs:  A,  simple  reflex  arc;  B,  chain  reflex;  C,  a  complex  system  illus- 
trating allied  and  antagonistic  reflexes  and  physiological  resolution;  D,  a 
complex  system  illustrating  allied  and  antagonistic  reflexes  with  a  final 
common  path;  E,  a  complex  system  illustrating  the  mechanism  of  physio- 
logical association.  A,  A,  association  neurons;  C,  C,  C",  CI,  and  C2,  centers 
(adjustors);  E,  E',  E",  El,  and  E2,  effectors;  FCP,  final  common  path; 
R,  R',  R",  Rl,  and  R2,  receptors. 

instance,  one  motor  system,  E2,  is  greatly  fatigued  and  the 
other  rested,  the  threshold  of  E2  will  be  raised  and  the  motor 
discharge  will  pass  to  £"1. 

Figure  18,  D  illustrates  the  converse  case,  where  two  recep- 
tors discharge  into  a  single  center,  which,  in  turn,  by  means  of  a 


62  INTRODUCTION    TO    NEUROLOGY 

final  common  path  (FCP)  excites  a  single  effector  (E).  If  the 
two  receptors  upon  stimulation  normally  call  forth  the  same 
response,  they  will  reinforce  each  other  if  simultaneously  stimu- 
lated, the  response  will  be  strengthened,  and  we  have  another 
type  of  allied  reflex.  But  there  are  cases  in  which  the  stimu- 
lation of  Rl  and  R2  (Fig.  18,  D)  would  naturally  call  forth 
antagonistic  reflexes.  Here,  if  they  are  simultaneously  stimu- 
lated, a  physiological  dilemma  will  again  arise  which  can  be 
resolved  only  by  one  or  the  other  afferent  system  getting  con- 
trol of  the  final  common  path. 

Figure  18,  E  illustrates  still  another  form  of  combination  of 
reflexes.  Here  there  are  connecting  tracts  {A,  A)  between  the 
two  centers  so  arranged  that  stimulation  of  either  of  the  two 
receptors  (^1  and  R2)  may  call  forth  a  response  in  either  one  of 
two  effectors  (£"1  and  E2).  These  responses  may  be  allied  or 
antagonistic,  and  much  more  complicated  reflexes  are  here  pos- 
sible than  in  any  of  the  preceding  cases. 

A  few  illustrations  of  the  practical  operation  of  these  types 
of  reflex  circuits  will  be  given  here  and  many  other  cases  are 
cited  throughout  the  following  discussions.  A  case  of  a  simple 
reflex  has  already  been  mentioned  in  the  sudden  twitch  of  the 
hand  in  response  to  a  painful  stimulation  of  the  skin.  The 
simplest  possible  mechanism  of  this  reaction  involving  only  two 
neurons  is  shown  in  Fig.  1  (p.  26).  In  actual  practice,  however, 
the  arrangement  figured  is  one  element  only  of  a  more  complex 
reaction  (see  p.  63).  Figure  19  illustrates  a  more  usual  form 
of  this  type  of  reaction,  where  a  series  of  three  or  more  neurons 
is  involved  and  at  least  two  cerebral  centers.  An  auditory  im- 
pulse coming  to  the  brain  from  the  ear  through  the  VIII  cranial 
nerve  terminates  in  a  primary  acoustic  center  in  the  superior 
olive  (a  deep  nucleus  of  the  medulla  oblongata,  see  p.  224), 
where  it  is  taken  up  by  an  intercalary  neuron  of  the  second 
order  and  transmitted  to  the  nucleus  of  the  VI  nerve.  The 
result  is  a  contraction  of  the  external  rectus  muscle  of  the  eye- 
ball, turning  the  eye  toward  the  side  from  which  the  auditory 
stimulus  was  received.  So  far  as  this  reaction  alone  is  con- 
cerned, it  is  a  simple  reflex,  but  in  practice  the  external  rectus 
muscle  of  one  eye  is  never  contracted  apart  from  the  other  five 
muscles  of  that  eye  and  all  six  muscles  of  the  other  eye.     In 


THE    REFLEX    CIRCITTTS 


63 


this  way  alone  can  conjugate  movements  of  the  two  eyes  be 
effected  for  the  accurate  fixation  of  the  gaze  upon  any  object. 
The  entire  system  of  conjugate  movements  is  also  entirely 
reflex  and  it  is  effected  by  an  exceedingly  complicated  arrange- 
ment of  nerve  tracts  and  centers,  of  which  the  superior  olive 
and  the  nucleus  of  the  VI  nerve  are  integral  parts. 

The  chain  reflex  (see  Fig.  18,  B)  is  a  very  common  and  a  very 
important  type.  Most  of  the  ordinary  acts  in  the  routine  of 
daily  life  employ  it  in  one  form  or  another,  the  completion  of 
one  stage  of  the  process  serving  as  the  stimulus  for  the  initia- 
tion of  the  next. 


3n  nerve 


Fig.  19. — Diagram  of  a  simple  auditory  reflex.  Upon. stimulation  of  the 
endings  of  the  VIII  nerve  in  the  ear  by  sound  waves,  a  nervous  impulse  may 
pass  to  the  superior  olive,  whence  it  is  carried  by  an  intercalary  neuron  of 
the  second  order'  to  the  nucleus  of  the  VI  nerve.  The  fibers  of  this  nerve 
end  on  the  external  rectus  muscle  of  the  eyeball. 

There  are  within  the  muscles  elaborate  sense  organs  (the 
muscle  spindles  and  their  associated  afferent  nerves,  see  p.  92), 
which  are  stimulated  by  the  contraction  of  the  muscle.  These 
afferent  nerves  of  the  muscle  sense  have  their  own  centers  of 
adjustment  within  the  central  nervous  system,  from  which  in 
turn  efferent  impulses  go  out  which  ultimately  reach  the  same 
muscles  from  which  the  sensory  impulses  came  in.  This,  of 
course,  is  a  variety  of  chain  reflex,  and  is  the  mechanism  by 
which  refined  movements  of  precision  are  executed,  where 
different  sets  of  muscles  must  work  against  each  other  in 
constantly  varying  relations  without  conscious  control.  In 
the  case  of  a  sustained  reflex  series  of  this  character  this  return 
flow  of  afferent  impulses  of  the  muscle  sense,  tendon  sense, 
etc.,  exerts  a  constant  influence  upon  the  center  which  receives 


64  INTRODUCTION  TO  NEUROLOGY 

the  initial  stimulus,  so  that  this  center  is  constantly  under  the 
combined  influence  of  the  external  stimulus  which  sets  the 
reflex  in  motion  and  the  internal  stimuli  arising  from  the 
muscles  themselves  (proprioceptors,  see  p.  92)  which  control 
its  course.  In  this  case  there  is  a  true  physiological  circuit 
rather  than  an  arc  or  segment  of  a  circuit,  as  is  commonly 
implied  in  the  expression  ''reflex  arc."  This  case  is  typical  of 
the  complex  reflexes  of  the  body  in  general,  and  for  this  and 
other  considerations  we  follow  the  usage  of  DeWey  (1893)  and 
term  the  mechanism  of  a  complete  reflex  a  "reflex  circuit" 
rather  than  an  arc  (see  C.  J.  Herrick,  1913,  and  p.  342). 

It  has  been  suggested  by  Loeb  also  that  many  instincts  are 
simply  complex  chain  reflexes.  Even  in  animals  whose  behav- 
ior is  so  complex  as  birds,  a  careful  analysis  of  the  cycle  of 
nest  building  and  rearing  of  young  reveals  many  clear  illus- 
trations of  this  principle  (see  the  works  of  F.  H.  Herrick,  cited 
at  the  end  of  this  chapter).  Each  step  in  the  cycle  is  a  neces- 
sary antecedent  to  the  next,  and  if  the  series  is  interrupted 
it  is  often  necessary  for  the  birds  to  go  back  to  the  beginning 
of  the  cycle.  They  cannot  make  an  intelligent  adjustment 
midway  of  the  series. 

The  complex  circuit  illustrated  by  Fig.  18,  C  presents  two 
possible  types  of  reaction,  either  allied  or  antagonistic  reflexes. 
The  former  case  is  illustrated  again  by  the  sudden  movement  of 
the  hand  in  response  to  a  painful  stimulation  of  the  skin.  This 
is  brought  about,  as  we  saw  in  considering  the  simple  reflex,  by 
a  contraction  of  the  arm  muscles.  But  the  muscles  which 
move  the  elbow-joint  are  not,  when  the  arm  is  at  rest,  entirely 
flaccid.  Both  flexors  and  extensors  are  always  contracted  to  a 
certain  degree,  one  balanced  against  the  other.  Now  at  the 
same  time  that  the  sensory  stimulus  from  R  (see  Fig.  18,  C) 
causes  the  contraction  of  the  flexor  muscle.  El,  it  also  causes 
the  relaxation  of  the  antagonistic  extensor,  E2,  the  two  efferent 
impulses  cooperating  to  effect  the  avoiding  reaction  as  rapidly 
as  possible.  In  the  antagonistic  reflexes  of  our  third  type 
the  physiological  resolution  involved  in  the  selection  of  one 
or  the  other  possible  reaction  always  involves  a  delay  in  the 
response  until  one  motor  pathway  dominates  the  system  to 
the  exclusion  of  the  other. 


THE    REFLEX   CIRCUITS 


65 


In  the  fourth  type  of  complex  reflexes  (see  Fig.  18,  D)  two 
different  sensory  paths  discharge  into  a  single  center,  from  which 
a  final  common  path  goes  out  to  the  effector.  This  mechan- 
ism also  provides  for  both  alhed  and  antagonistic  reflexes,  A 
very  simple  apparatus  for  this  type  of  reflex  is  found  in  the  roof 
of  the  midbrain  of  the  lowly  amphibian,  the  common  mud 
puppy,  Necturus.  Here  the  upper  part  of  the  midbrain  roof 
receives  optic  fibers  from  the  optic  tracts,  while  the  lower  part 
receives  fibers  from  the  primary  acoustic  and  tactile  centers 


MOTOR 

/in  nerve  center 

Fig.  20. — Diagram  of  a  cross-section  through  the  midbrain  of  Necturus, 
illustrating  a  single  correlation  neuron  of  the  midbrain  roof.  One  dendrite 
spreads  out  in  the  optic  center  among  terminals  of  the  optic  tracts;  another 
dendrite  similarly  spreads  out  in  the  acoustic  and  tactile  center.  The  axon 
descends  to  connect  with  the  motor  neurons  of  the  III  nerve.  For  the  details 
of  this  apparatus  see  Herrick  (1917). 


(Fig.  20).  A  single  neuron  of  the  midbrain  may  send  one 
dendrite  downward  to  receive  acoustic  or  tactile  stimuli  (or 
both  of  these),  and  another  dendrite  upward  to  receive  optic 
stimuli.  If  the  animal  receives  visual  and  auditory  stimuli 
simultaneously,  the  intercalary  neuron  of  the  midbrain  may 
be  excited  by  both  sets  of  stimuli.  Its  discharge  through  the 
axon  to  the  motor  organs  of  response  (say  to  the  eye  muscles  bj'' 
way  of  the  III  nerve,  as  in  Fig.  20)  will  be  the  physiological 
resultant  of  both  sets  of  excitations.     If  they  reinforce  each 


66 


INTRODUCTION   TO    NEUROLOGY 


other,  the  discharge  will  be  stronger  and  more  rapid;  if,  on  the 
other  hand,  they  tend  to  produce  antagonistic  responses, 
there  will  be  an  inhibition  of  the  response  or  a  delay  until 
one  or  the  other  stimulus  obtains  the  mastery. 

Yerkes  has  given  a  striking  illustration  of  this  method  of  re- 
inforcement of  stimuli  in  his  experiments  on  the  sense  of  hear- 
ing in  frogs.  The  reflex  mechanism  of  touch,  hearing,  and 
vision  in  the  midbrain  of  the  frog  is  similar  to  that  of  Necturus 
as  described  above  (Fig.  20).  Yerkes  found  that  frogs  under 
laboratory  conditions  do  not  ordinarily  react  at  all  to  sounds 


midbrain 


££[£^ralhemisphere 


Fig.  21. — Diagram  of  some  conduction  paths  in  the  brain  of  Nectufus, 
seen  in  longitudinal  section.  From  the  medulla  oblongata  an  acoustic 
impulse  may  be  carried  forward  through  the  neuron  A  to  the  midbrain, 
whose  neurons,  B,  are  of  the  type  shown  in  Fig.  20,  receiving  both  acoustic 
and  optic  impulses.  This  neuron,  B,  may  discharge  downward  through  the 
tract  S  to  the  motor  nuclei  of  the  III,  V,  VII,  etc.,  nerves,  or  it  may  dis- 
charge upward  to  a  neuron  of  the  thalamus,  C,  which  also  receives  descend- 
ing impulses  from  the  cerebral  hemisphere  through  the  neuron,  D,  and,  in 
turn,  discharges  through  the  motor  tract,  S. 


alone,  but  that  they  do  react  to  tactual  and  visual  stimuli. 
When  these  reactions  are  carefully  measured,  it  is  found  that 
the  sound  of  an  electric  bell  occurring  simultaneously  with  a 
tactual  or  visual  stimulus  markedly  increases  (reinforces) 
the  strength  of  the  reaction. 

The  reflex  centers  of  the  midbrain  are  further  comphcated  by 
the  fact  that  the  efferent  tract  from  the  sensory  centers  above 
the  aqueduct  of  Sylvius  is  not  simple  as  diagrammed  in  Fig. 
20,  but  it  divides  into  a  descending  and  an  ascending  path,  as 
shown  by  the  neuron  B  of  Fig.  21.     The  descending  path 


THK    REFLEX    CIRCUITS  67 

connects  directly  with  motor  centers,  including  the  oculomotor, 
bulbar,  and  spinal  motor  nuclei  (Fig.  21,  *S'),  while  the  ascend- 
ing path  enters  the  thalamus,  where  associations  of  a  still 
higher  order  are  effected  through  the  thalamic  neuron,  C. 
Here  again  is  introduced  a  physiological  choice  or  dilemma; 
the  response  is  not  a  simple  mechanical  resultant  of  the  inter- 
acting stimuli,  but  its  character  may  be  influenced  by  variable 
physiological  states.  The  invariable  type  of  action  is  replaced 
by  a  relatively  variable  or  labile  type  (see  p.  32).  In  the 
thalamus  the  nervous  impulse  is  again  subjected  to  modifica- 
tion under  the  influence  of  a  still  greater  variety  of  afferent 
impulses,  for  these  centers  receive  all  sensory  types  found  in 
the  midbrain,  and,  in  addition,  important  descending  tracts 
from  the  cerebral  hemispheres  (in  lower  vertebrates  the  latter 
are  chiefly  olfactory). 

The  more  complicated  associations  are  effected  by  arrange- 
ments of  correlation  tracts  and  centers  illustrated  in  the  sim- 
plest possible  form  by  Fig.  18,  E.  The  mode  of  operation  of 
such  a  system  may  be  illustrated  by  an  example :  A  collie  dog 
which  I  once  owned  acquired  the  habit  of  rounding  up  my 
neighbor's  sheep  at  very  unseasonable  times.  The  sight  of 
the  flock  in  the  pasture  (stimulus  Rl,  Fig.  18,  E)  led  to  the 
pleasurable  reaction  (El)  of  chasing  the  sheep  up  to  the  barn- 
yard. It  became  necessary  to  break  up  the  habit  at  once  or 
lose  a  valuable  dog  at  the  hands  of  an  angry  farmer  with  a 
shotgun.  Accordingly,  I  walked  out  to  the  pasture  with  the 
dog.  She  at  once  brought  in  the  sheep  of  her  own  accord  and 
then  ran  up  to  me  with  every  expression  of  canine  pride  and 
self-satisfaction,  whereupon  I  immediately  gave  her  a  severe 
whipping  (stimulus  R2).  This  called  forth  the  reaction  {E2) 
of  running  home  and  hiding  in  her  kennel.  The  next  day 
(the  dog  and  I  having  meanwhile  with  mutual  forgiveness 
again  arrived  at  friendly  relations)  we  took  a  walk  in  a  different 
direction,  in  the  course  of  which  we  unexpectedly  met  another 
flock  of  sheep.  At  sight  of  these  the  dog  immediatel}^,  with 
no  word  from  me,  put  her  tail  between  her  legs,  ran  home  as 
fast  as  possible,  and  hid  in  her  kennel.  Here  the  stimulus 
Rl  lod  not  to  its  own  accustomed  response,  £"1,  but  to  E2, 
evidently  under  the  influence  of  vestigeal  traces  of  the  previous 


68  INTRODUCTION  TO  NEUROLOGY 

day's  experience,  wherein  the  activities  of  CI  and  C2  were 
related  through  the  associational  tract  {A,  A)  passing  between 
them. 

In  the  case  of  the  dog's  experience  just  described  the  neural 
mechanism  was  undoubtedly  much  more  complex  than  our  dia- 
gram, though  similar  in  principle,  and  the  associative  memory 
process  involved  was  probably  vividly  conscious  (cf.  p.  329). 
But  the  simpler  types  of  ''associative  memory"  which  have 
been  experimentally  demonstrated  in  many  of  the  lower  or- 
ganisms may  involve  no  more  complex  mechanism  than  this 
diagram,  and  it  is  by  no  means  certain  that  any  conscious 
process  is  there  present. 

From  the  preceding  account  it  is  clear  that  isolated  individual  re- 
flexes are  rarely  seen  in  ordinary  behavior,  but  that  these  are  usually  com- 
pounded so  as  to  mask  their  specific  characteristics.  Clinical  neurolo- 
gists find  that  the  reflexes  give  very  valuable  signs  of  the  health  or  dis- 
ease of  particular  parts  of  the  nervous  system  and  they  have,  accordingly, 
developed  special  tests  for  characteristic  reflex  signs,  such  as  the  wink  re- 
flex, pupillary  reflex,  knee  jerk,  etc. 

Since  many  of  the  reflexes  are  normally  under  continuous  control 
(either  conscious  or  unconscious)  by  the  cerebral  cortex,  the  physiolo- 
gists have  investigated  the  reflexes  of  particular  parts  of  the  nervous 
system  by  separating  them  in  the  anesthetized  animal  from  their  cortical 
connections.  Thus,  if  the  upper  part  of  the  spinal  cord  is  cut  across,  we 
have  the  so-called  spinal  animal  in  which  spinal  reflexes  may  be  studied 
without  the  complications  arising  from  the  cerebral  connections. 

The  "spinal  frog"  exhibits  no  power  of  spontaneous  movement  apart 
from  direct  peripheral  excitation;  but  pinching  the  toes  will  cause  a 
reflex  withdrawal  of  the  foot,  and  many  other  perfectly  coordinated  move- 
ments may  be  called  forth  by  appropriate  stimulation.  The  reflexes 
of  the  "spinal  dog"  have  been  very  carefully  investigated  by  Sherring- 
ton (see  his  Integrative  Action  of  the  Nervous  System)  and  various 
coordinated  movements  characteristic  of  the  locomotor  reflexes,  scratch- 
ing, etc.,  have  been  thus  experimentally  studied  and  the  details  of 
their  neuromuscular  mechanisms  determined. 

In  the  frog  whose  spinal  cord  has  been  cut  across  there  is  a  transient 
disturbance  of  the  lower  spinal  reflexes  which,  however,  soon  show  very 
perfect  co5rdination.  In  the  spinal  dog  the  reflex  disturbance  is  greater 
and  more  enduring,  though  ultimately  very  complete  reflex  coordination 
is  regained.  But  in  man  after  complete  transverse  section  of  the  spinal 
cord  there  is  loss  of  nearly  all  spinal  reflexes  and  very  few  of  these  can 
ever  be  regained. 

This  interference  with  spinal  reflexes  by  cutting  the  connection  be- 
tween the  spinal  cord  and  the  brain  is  known  as  spinal  shock,  and  the 
fact  that  spinal  shock  is  more  severe  and  more  permanent  as  we  pass  from 
lower  to  higher  vertebrates  suggests  that  in  the  course  of  evolution  the 
brain  (especially  the  cerebral  cortex)  has  acquired  an  increasingly  greater 
control  over  the  lower  and  more  primitive  reflex  centers.  There  is  in- 
dependent evidence  that  this  is  true  (see  Pike,  1909  and  1912). 


T?IE    REFLEX    CTRCTTITft  69 

By'.mcaiis  of  numerous  experiments  on  animals  and  pathological 
observations  on  man  the  locations  of  the  centers  of  adjustment  for  many 
individual  reflexes  have-  l)een  determined.  Charts  illustrating  the  pre- 
cise segments  of  the  spinal  cord  which  control  the  various  reflexes  f)f  the 
trunk  and  limbs  have  been  constructed  (c.  q.,  Reid's  chart,  p.  14S. 
Such  charts  are  published  in  the  larger  manuals  of  neurology  and  these 
are  of  the  greatest  practical  value  to  the  physician  and  surgeon  in  en- 
abling them  to  determine  the  exact  location  of  an  injury  which  causes 
disorder  of  the  reflexes,  as  well  as  of  voluntary  movement  and  conscious 
sensibility. 

It  must  be  kept  in  mind  that  in  higher  vertebrates  all  parts 
of  the  nervous  system  are  bound  together  by  connecting  tracts 
(internuncial  pathways).  Some  of  these  tracts  are  long,  well- 
defined  bundles  of  myelinated  fibers  whose  connections  are 
such  as  to  facilitate  uniform  and  clear-cut  responses  to  stimu- 
lation. Others  are  very  diffuse  and  poorly  integrated.  Per- 
meating the  entire  central  nervous  system  is  an  entanglement 
of  very  delicate  short  unmyelinated  fibers.  This  nervous  felt- 
work  (neuropil)  is  much  more  highly  developed  in  some  parts 
of  the  brain  than  in  others.  It  is  not  well  adapted  to  conduct 
definite  nervous  impulses  for  long  distances,  but  it  may  serve 
to  diffuse  or  irradiate  such  impulses  widely.  Where  tissue  of 
this  sort  is  mingled  with  myelinated  fibers  it  is  termed  the 
"  reticular  formation "  (see  pp.  138,  172,  338). 

These  manifold  connections  are  so  elaborate  that  every  part 
of  the  nervous  system'is  in  nervous  connection  with  every  other 
part,  directly  or  indirectly.  This  is  illustrated  by  the  way  in 
which  the  digestive  functions  (which  normally  are  quite  autono- 
mous, the  nervous  control  not  going  beyond  the  sympathetic 
system,  see  p.  268)  may  be  disturbed  by  mental  processes 
whose  primary  seat  may  be  in  the  association  centers  of  the 
cerebral  cortex;  and  also  by  the  way  in  which  strj^chnin- 
poisoning  seems  to  lower  the  neural  resistance  everywhere,  so 
that  a  very  sHght  stimulus  may  serve  to  throw  the  whole  body 
into  convulsions. 

It  follows  that  the  localization  of  cerebral  functions  can  be 
only  approximate.  Every  normal  activity  has  what  Sherring- 
ton calls  its  reflex  pattern,  whose  anatomical  basis  is  a  definite 
reflex  path;  but  the  stimulus  is  rarely  simple  and  the  nervous 
discharge  irradiates  more  or  less  widely,  so  that  the  activity  is 
by  no  means  limited  to  the  part  which  gives  the  act  its  reflex 


70  INTRODUCTION  TO  NEUROLOGY 

pattern.  Moreover,  neither  the  stimulus  complex  nor  the 
character  of  the  irradiation  will  be  repeated  exactly  in  any 
higher  animal,  so  that  the  precise  nature  of  the  response  cannot 
in  any  case  be  infallibly  predicted  except  under  experimental 
conditions  (and  not  always  then). 

Our  picture  of  the  reflex  act  in  a  higher  animal  will,  then, 
include  a  view  of  the  whole  nervous  system  in  a  state  of  neural 
tension.  The  stimulus  disturbs  the  equilibrium  at  a  definite 
point  (the  receptor),  and  the  wave  of  nervous  discharge  thus 
set  up  irradiates  through  the  complex  lines  determined  by  the 
neural  connections  of  the  receptor.  If  the  stimulus  is  weak 
and  the  reflex  path  is  simple  and  well  insulated,  a  simple 
response  may  follow  immediately.  Under  other  conditions 
the  nervous  discharge  may  be  inhibited  before  it  reaches  any 
effector,  or  it  may  irradiate  widely,  producing  a  very  complex 
reflex  pattern.  In  the  former  case  the  neural  equilibrium 
will  be  only  locally  disturbed;  in  the  latter  case  almost  the 
whole  nervous  system  may  participate  in  the  reaction,  a  part 
focal  and  sharply  defined  and  the  rest  marginal,  diffuse,  and 
exercising  more  or  less  of  inhibitory  or  reinforcing  control 
on  the  final  reaction. 

The  mechanism  of  the  reflex  should  not  be  regarded  as  an 
open  channel  through  which  energy  admitted  at  the  receptive 
end-organ  is  transmitted  to  be  discharged  into  the  effector 
organ.  It  is  rather  a  complex  apparatus  containing  reserves 
of  potential  energy  which  can  be  released  upon  the  application 
of  an  adequate  stimulus  in  accordance  with  a  pattern  deter- 
mined by  the  inherent  structure  of  the  apparatus  itself.  In 
other  words,  the  nervous  discharge  is  not  a  mere  transmission 
of  the  energy  of  the  stimulus,  but  it  imphes  active  consumption 
of  material  and  release  of  energy  (metabolism)  within  both 
the  nerve  centers  and  the  nerve-fibers.  The  energy  acting 
upon  the  effector  organ  may,  therefore,  be  different  in  both 
kind  and  amount  from  that  apphed  to  the  receptive  end-organ. 
The  response  likewise  involves  the  liberation  of  the  latent 
energy  of  the  effector  (muscle  or  gland),  the  nervous  impulse 
serving  merely  to  release  the  trigger  which  discharges  this 
reserve  energy. 


THE    REFLEX    CIRCUITS  71 

Further  consideration  of  the  nature  of  the  mechanism  of  the  more  com- 
plex reflexes  brings  out  certain  physiological  differences  between  the 
afferent  ("sensory")  and  the  efferent  limbs  of  the  arc.  To  any  particu- 
lar complex  of  stimuli  there  is  a  single  most  appropriate  response. 
It  is  the  function  of  the  correlation  centers  to  receive  the  afferent  nerv- 
ous impulses  from  the  sense  organs,  and  as  a  result  of  the  mutual  inter- 
action of  these  impulses  to  integrate  them  and  direct  the  discharge  into 
the  particular  final  common  path  which  will  call  forth  the  appropriate 
response.  These  correlating  mechanisms  are  sometimes  extraordinarily 
complex  and  their  activities  require  a  very  appreciable  time.  Here, 
then,  is  the  explanation  of  the  central  delay  or  pause  which  is  charac- 
teristic of  all  reactions  involving  the  correlation  centers  (see  p.  104). 
This  process  of  correlation  and  integration  of  sensory  impulses  is  effected 
on  the  afferent  side  of  the  reflex  arc,  and  it  results  in  establishing  the 
character  of  the  response  to  follow  before  the  turning  point  into  the  effer- 
ent path  has  been  reached. 

The  efferent  side  of  the  arc,  on  the  other  hand,  has  merely  to  transmit 
the  necessary  nervous  impulses  to  the  motor  neuron  systems  required  for 
the  execution  of  the  movement  in  the  shortest  possible  time.  The  so- 
called  motor  centers,  accordingly,  discharge  by  simple  and  very  direct 
nervous  pathways  with  the  minimum  number  of  synapses  between  them 
and  the  organs  of  response.  This  is  the  neurological  basis  of  the  distinc- 
tion made  on  p.  36  between  correlation  and  coordination. 

The  preceding  remarks  apply  to  the  mechanisms  of  conscious  actions  as 
well  as  to  the  reflexes.  The  cerebral  cortex  as  a  whole  is  developed  within 
the  area  of  sensory  correlation  tissue  above  the  sulcus  limitans  (p.  129, 
cf.  also  p.  340).  The  "motor  centers"  in  the  precental  gyrus  of  the 
cortex  represent  the  turning  point  from  the  afferent  to  the  efferent 
segments  of  the  nervous  circuits,  and  from  this  point  to  the  lower 
motor  centers  the  pathway  is  as  short  and  direct  as  possible  with  no 
interruption  by  synapses.  The  chief  efferent  pathway  for  voluntary 
motor  impulses  is  the  pyramidal  tract  (pp.  142,  198,  317,  and  Fig.  64, 
p.  152). 

The  studies  of  Herrick  and  Coghill  have  shown  that  in  the 
development  of  the  nervous  system  of  Amphibia  the  first  reflex 
circuits  to  come  to  maturity  are  made  up  of  rather  complex 
chains  of  neurons  so  arranged  as  to  permit  of  onlj^  one  type  of 
response,  viz.,  a  total  reaction  (the  swimming  movement), 
from  all  possible  forms  of  stimulation,  and  that  in  successive 
later  stages  this  generalized  type  is  gradually  replaced  by  a 
series  of  special  reflexes  involving  more  diversified  movements. 
Parallel  with  this  process  the  higher  correlation  centers  are 
developed  for  the  integration  of  the  several  special  reflexes 
into  complex  action  systems.  The  simple  reflex  arc,  as 
illustrated  in  Fig.  1  (p.  26),  which  is  adapted  for  the  execution 
of  a  single  movement  in  response  to  a  particular  stimulus,  is 
the  final  stage  in  this  developmental  process,  whose  initial 


72  INTRODUCTION  TO  NEUROLOGY 

stages  are  much  more  complex  and  diffuse  arrangements  of 
neurons  adapted  for  total  reactions  of  a  more  general  sort. 

We  have  just  described  the  mechanisms  of  certain  reflexes. 
The  question  at  once  arises,  In  what  sense  do  we  know  the 
mechanism  of  a  nervous  reaction?  Certainly  not  in  the  sense 
that  we  understand  all  of  the  factors  involved  in  nervous  con- 
duction and  correlation.  But  we  do  have  a  practical  knowl- 
edge of  the  combinations  of  neurons  necessary  to  effect  certain 
definite  results,  much  as  the  practical  electrician  may  be  able 
to  wind  a  dynamo  or  build  a  telephone,  even  though  his  knowl- 
edge of  the  theory  of  electricity  be  very  small. 

Summary. — The  reflex  arcs  or  reflex  circuits  rather  than 
the  neurons  of  which  these  circuits  are  composed  are,  from 
the  physiological  standpoint,  the  most  important  units  of  the 
nervous  system.  Reflex  acts  are  to  be  distinguished,  on  the 
one  hand,  from  the  simpler  non-nervous  reactions  known  as 
tropisms  and  taxes,  and,  on  the  other  hand,  from  voluntary 
acts  and  acquired  automatisms.  Many  instincts  are  chain 
reflexes  of  very  complex  sorts,  the  completion  of  one  reaction 
serving  as  the  stimulus  for  the  next,  and  so  on  in  series.  The 
simplest  true  reflex  requires  a  receptor,  a  center  or  adjustor, 
an  effector,  and  the  afferent  and  efferent  conductors  which  put 
the  center  into  physiological  relation  with  the  receptor  and  the 
effector  respectively.  Five  types  of  reflex  circuits  were  distin- 
guished (see  Fig.  18)  and  illustrations  of  them  given.  All  of 
the  reflex  centers  are  interconnected  by  systems  of  fibers,  either 
in  the  form  of  definite  tracts  or  else  by  more  diffuse  connections 
in  the  neuropil.  Localization  of  cerebral  function  is,  therefore, 
only  approximate,  with  the  possibihty  of  all  sorts  of  intercon- 
nection of  different  reflex  systems  as  occasion  may  require. 
This  is  the  neurological  basis  of  the  greater  plasticity  of 
behavior  of  higher  vertebrates  as  contrasted  with  invertebrates 
and  lower  vertebrates. 

Literature 

Dewey,  J.  1893.  The  Reflex  Arc  Concept  in  Psychology,  Psychol. 
Review,  vol.  iii,  p.  357. 

Herrick,  C.  Judson.  1913.  Some  Reflections  on  the  Origin  and 
Significance  of  the  Cerebral  Cortex,  Jour,  of  Animal  Behavior,  vol.  iii, 
pp.  222-236. 


THE    REFLEX    CIRCUITS  73 

Herrick,  C.  Judson.  1917.  The  Internal  Structure  of  the  Midbrain 
and  Thalamus  of  Necturus,  Jour.  Comp.  Neur.,  vol.  xxviii,  pp.  21.5-348. 

Herrick  C.  Judson  and  Coghill,  G.  E.  191.5.  The  Development  of 
Reflex  Mechanisms  in  Amblystoma,  Jour.  Comp.  Neur.,  vol.  xxv,  pp. 
65-85. 

Herrick,  F.  H.  1905.  The  Home  Life  of  Wild  Birds.  Revised 
edition,  New  York. 

— .  1907.  Analysis  of  the  Cyclical  Instincts  of  Birds,  Science, 
N.  S.,  vol.  xxv,  pp.  725,  726;  and  Jour.  Comp.  Neur.,  vol.  xvii,  pp.  194, 
195. 

— .  1907.  The  Blending  and  Overlap  of  Instincts,  Science,  N.  S., 
vol.  xxv,  pp.  781,  782;  and  Jour.  Comp.  Neur.,  vol.  xvii,  pp.  195-197. 

— .  1908.  The  Relation  of  Instinct  to  Intelligence  in  Birds,  Science, 
N.  S.,  vol.  xxvii,  pp.  847-850. 

Hough,  Th.  1915.  The  Classification  of  Nervous  Reactions,  Sci- 
ence, N.  S.,  vol.  xh,  pp.  407-418. 

Jennings,  H.  S.  1905.  The  Basis  for  Taxis  and  Certain  Other  Terms 
in  the  Behavior  of  Infusoria,  Jour.  Comp.  Neur.,  vol.  xv,  pp.  138-143. 

— .     1906.     The  Behavior  of  Lower  Organisms,  New  York. 

— .  1908.  The  Interpretation  of  the  Behavior  of  the  Lower  Organ- 
isms, Science,  N.  S.,  vol.  xxvii.  No.  696,  p.  698-710. 

— .  1909.  Tropisms,  Comptes  Rendus  VI.  Congres  Internat.  de 
Psychol.,  Geneva,  pp.  307-324. 

LoEB,  J.  1909.  Comparative  Physiology  of  the  Brain  and  Compara- 
tive Psychology,  New  York. 

— .     1912.     The  Mechanistic  Conception  of  Life,  Chicago. 

Pike,  F.  H.  1909.  Studies  in  the  Physiology  of  the  Central  Nervous 
System,  I.  The  General  Phenomena  of  Spinal  Shock,  Am.  Jour.  Phy- 
siol., vol.  xxiv,  pp.  124-152. 

— .  1912.  Do.  II.  The  Effect  of  Repeated  Injuries  to  the  Spinal 
Cord  during  Spinal  Shock,  Am.  Jour.  Physiol.,  vol.  xxx,  pp.  436-450. 

Sherrington,  C.  S.  1906.  The  Integrative  Action  of  the  Nervous 
System,  New  York. 

Yerker,  R.  M.  1905.  The  Sense  of  Hearing  in  Frogs,  Jour.  Comp. 
Neur.,  vol.  xv,  pp.  279-304. 


CHAPTER  V 

THE  RECEPTORS  AND  EFFECTORS 

In  the  further  study  of  the  nervous  system  as  the  apparatus 
of  adjustment  between  the  activities  of  the  body  and  those  of 
environing  nature,  our  first  task  is  the  analysis  of  the  recep- 
tors (that  is,  the  sense  organs);  for  these  are  the  only  places 
through  which  the  forces  of  the  world  outside  can  reach  the 
nervous  system  in  order  to  excite  its  activity. 

."The  world  is  so  full  of  a  number  of  things 
I'm  sure  we  should  all  be  as  happy  as  kings." 

But  in  order  to  attain  this  fortunate  result  it  is  necessary  that 
we  should  be  able  to  discriminate  the  essential  from  the  unim- 
portant elements  of  this  environing  complex,  and  to  adjust 
our  own  behavior  in  relation  thereto. 

Protoplasm  in  its  simplest  form  is  sensitive  to  some  sorts  of 
mechanical  and  chemical  stimulation.  In  fact,  as  we  have 
seen,  all  of  the  so-called  nervous  functions  are  implicit  in  undif- 
ferentiated protoplasm.  But  the  bodies  of  aU  but  a  few  of  the 
lowest  organisms  are  protected  by  some  sort  of  a  shell  or  cuticle 
from  excessive  stimulation  from  the  outside,  and  individual 
parts  of  the  surface  are  then  differentiated  in  such  a  way  as  to 
be  sensitive  to  only  one  group  of  excitations  while  remaining 
insensitive  to  all  other  forms.  Thus  arose  the  sense  organs, 
each  of  which  consists  essentially  of  specialized  protoplasm 
which  is  highly  sensitive  to  some  particular  form  of  energy 
manifestation,  but  relatively  insensitive  to  other  forms  of 
stimulation.  Each  sense  organ  possesses,  in  addition,  certain 
accessory  parts,  adapted  to  concentrate  the  stimuU  upon  the 
essential  sensitive  protoplasm,  to  intensify  the  force  of  the 
stimulus,  or  to  so  transform  the  energy  of  the  stimulus  as  to 
enable  it  to  act  more  efficiently  upon  the  essential  end-organ. 

Sherrington  states  the  distinctive  characteristic  of  the  sense 

74 


THE  RECEPTORS  AND  EFFECTORS  75 

organs  in  this  form,  "The  main  function  of  the  receptor  is, 
therefore,  to  lower  the  threshold  of  excitahilitij  of  the  arc  for  one 
kind  of  stimulus  and  to  heighten  it  for  all  others."  The  selective 
function  of  the  receptors  is  illustrated  by  a  consideration  of  the 
different  forms  of  vibratory  energy  which  pervade  the  environ- 
ment in  which  we  live. 

There  are,  first,  rhythmically  repeated  mechanical  impacts 
perceived  through  the  sense  of  touch.  This  series  of  tactile 
sensations  extends  from  a  single  isolated  contact  at  one  extreme 
to  rhythmically  repeated  contacts  touching  the  skin  as  fre- 
quently as  1552  vibrations  per  second, 

A  second  series  of  vibratory  phenomena  is  presented  by  the 
mechanical  vibrations  of  the  surrounding  medium  perceived 
subjectively  as  sound.  Out  of  the  entire  series  of  such  vibra- 
tions of  all  possible  frequencies  the  human  ear  is  sensitive  to  a 
series  of  approximately  ten  octaves  from  about  30  (in  some 
cases  12)  to  about  30,000  (in  some  cases  50,000)  vibrations  per 
second  (wave  lengths  from  1228  cm.  or  40  ft.  to  1.3  cm.  or  .5 
inch  in  length).  To  all  other  vibrations  it  is  insensitive. 
Within  this  range  the  average  human  ear  can  discriminate  some 
11,000  different  pitch  qualities  (Titchener). 

Subjectively,  the  series  of  tone  sensations  is  broken  up  into 
a  number  of  octaves,  and  it  is  found  that  a  given  tone  of  the 
musical  scale  is  excited  by  vibrations  of  exactly  twice  the  fre- 
quency which  excites  the  corresponding  tone  of  the  next  lower 
octave.  By  analogy  with  this  arrangement  all  series  of  phj^s- 
ical  vibrations  are  sometimes  spoken  of  as  divisible  into  oc- 
taves, the  octave  being  defined  as  those  vibration  frequencies 
which  lie  between  a  given  rate  and  twice  that  rate  or  half  that 
rate. 

A  third  type  of  vibratory  phenomena  is  presented  by  the 
much  more  rapid  series  of  so-called  ethereal  vibrations,  or 
waves  in  immaterial  media.  The  lower  members  of  this  series 
are  the  Hertzian  electric  waves;  the  higher  members  are  the 
a:-rays.  Between  these  extremes  lie  waves  perceived  as  radi- 
ant heat,  the  light  waves,  and  the  ultra-'V'iolet  rays  of  the 
spectrum.  This  series  of  ethereal  vibrations  maj^  extend 
farther  indefinitely  both  downward  and  upward,  but  of  its 
ultimate  limits  we  have  no  knowledge. 


76  INTRODUCTION  TO  NEUROLOGY 

There  is  no  human  sense  organ  which  can  respond  directly  to 
the  electric  waves,  the  ultra-violet  rays,  and  the  x-rays. 
These  have,  accordingly,  remained  wholly  unknown  to  us  until 
revealed  indirectly  by  the  researches  of  the  physical  labora- 
tories. Some  ten  octaves  of  this  series  are  contained  in  the 
solar  spectrum,  from  an  infra-red  wave  length  of  about  .1  mm. 
to  an  ultra-violet  wave  length  of  .00035  mm.  The  light  from 
metallic  arcs  and  from  incandescent  gases  has,  however,  been 
found  to  contain  wave  lengths  as  short  as  .00006  mm.  The 
human  eye  is  sensitive  to  something  over  one  octave  of  this 
series  (waves  from  .0008  to  .0004  mm.  in  length,  whose  rates  lie 
between  400,000  and  800,000  billions  of  vibrations  per  second), 
with  six  octaves  in  the  infra-red  and  three  in  the  ultra-violet. 
The  lower  members  of  this  series  of  vibrations  of  the  solar 
spectrum,  and  to  a  less  extent  the  higher  also,  are  capable  of 
stimulating  the  temperature  organs  of  the  skin. 

Thus  it  appears  that  of  the  complete  series  of  ethereal  vibra- 
tions, we  can  sense  directly  only  about  one  octave  by  the  eye 
and  a  number  of  others  through  the  sense  organs  for  tempera- 
ture in  the  skin,  while  to  the  lowest  and  highest  members  of 
the  series  our  sense  organs  are  entirely  insensitive.  The 
sensitivity  of  the  skin  to  these  vibrations  is  limited  subjectively 
to  a  small  range  of  temperature  sensations,  while  the  retinal 
excitations  give  us  subjectively  an  extensive  series  of  sensations 
of  color  and  brightness.  The  human  eye  can  discriminate  from 
150  to  230  pure  spectral  tints,  besides  various  degrees  of  in- 
tensity and  purity  of  tone,  making  a  total  of  between  500,000 
and  600,000  possible  discriminations  by  the  visual  organs  (von 
Kries).  Some  of  the  preceding  data  are  summarized  in  the 
table'^  on  page  77. 

Similarly,  the  chemical  senses,  taste  and  smell,  reveal  to  us 
only  a  very  small  number  out  of  the  total  series  of  actual  excita- 

^  In  the  preparation  of  this  table  I  have  been  assisted  by  Professor 
R.  A.  Millikan,  of  the  University  of  Chicago,  whose  kindness  I  gratefully 
acknowledge.     The  figures  given  are  based  upon  the  formula — 

velocity 

1 Tu   =  rate 

wave  length 

and  the  velocity  of  transmission  is  taken  as  3  X  10^°  cm.  per  second.  The 
actual  velocity  of  light  waves  as  worked  out  experimentally  by  Michelson 
is  299,853  kilometers  per  second. 


THE    RECEPTORS   AND    EFFECTORS 
TABLE   OF  PHYSICAL   VIBRATIONS 


77 


Physical 
-  process. 

Wave 
length. 

Number  of  vibrations 
per  second. 

Receptor.!  Sensation. 

1 

Mechanical 

From  very  slow 

to 
1552  per  second. 

Skin. 

Touch  and 

contact. 

pressure. 

Below  12,280  mm. 

Below  30  per  second. 

None. 

None. 

Waves  in 
material 
media. 

12,280  mm. 

to 

13  mm. 

30  per  second 

to 

30,000  per  second. 

Internal 
ear. 

Tone. 

Above  13  mm. 

Above  30,000  per  second.       |     None. 

None. 

00  to  .1  mm. 
(electric  waves). 

Oto  SOOObiUion  (3X10i2). 

None. 

None. 

.1  mm. 

to 
.0004  mm. 

SOOObilUon  (3Xl0i=) 

to                                  Skin. 
800,000  bilUon  (8X10"). 

Radiant 
heat. 

Ether  waves. 

.0008  mm. 

to 
.0004  mm. 

400,000  billion  (4X10») 

to                                Retina. 

800,000  billion  (8X10"). 

Light  and 
color. 

.0004  mm. 

to 

.000059  mm. 

(ultra-\'ioIet-rays) . 

800,000  bilUon  (8X10") 

to 

5,100,000  billion  (5.1  X 10"). 

None. 

None. 

.0000008  mm. 

to 

.00000005  mm. 

(x-rays). 

400,000,000  biUion  (4X10'^) 

to 

6,000,000,000  bilKon  (6X10«). 

None. 

None. 

tions  to  which  our  sense  organs  are  exposed.  Our  organs  of 
taste,  in  fact,  can  respond  to  only  four  types  of  chemical  sub- 
stances, with  only  four  subjective  sense  quahties,  viz.,  sour, 
salty,  sweet,  bitter.  The  organs  of  smell  respond  to  a  larger 
range  of  chemical  stimuli  and  to  far  greater  dilutions,  i.  e., 
the  threshold  of  sensation  is  far  lower  for  smell  than  for  taste. 

Manj^  of  the  lower  animals  have  very  different  hmits  of  sus- 
ceptibility to  the  kinds  of  stimulation  which  we  have  just  been 
considering,  and  in  some  cases  they  have  sense  organs  wliich  are 
attuned  to  respond  to  a  quite  different  series  of  environmental 
factors  than  are  our  own,  as,  for  example,  the  lateral  line  sense 
organs  of  fishes.  We  can  form  no  idea  how  the  world  appears 
to  such  organisms  except  in  so  far  as  their  sensory  equipment 
is  analogous  with  our  own. 

From  these  illustrations  it  is  plain  that  the  sensory  equip- 
ment of  the  human  body  is  adapted  to  respond  directly  to  only 


78  INTRODUCTION  TO  NEUROLOGY 

a  limited  part  of  the  environing  energy  complex,  the  remainder 
having  Uttle,  if  any,  practical  significance  in  the  natural  en- 
vironment of  primitive  man.  During  the  progress  of  the  de- 
velopment of  human  culture  mankind  has  very  considerably 
widened  his  contact  with  the  environment  by  artificial  aids  to 
his  sense  organs.  The  range  of  Adsion  has  been  extended  by  the 
microscope  and  the  telescope,  and  of  hearing  by  the  micro- 
phone and  the  telephone.  The  photographic  plate  enables 
him  to  extend  his  knowledge  of  the  solar  spectrum  beyond  its 
visible  limits,  and  the  Marconi  wireless  apparatus  brings  the 
Hertzian  electric  waves  under  his  control  and  thus  enables  him 
to  put  a  girdle  round  about  the  earth  in  less  than  Puck's  forty 
minutes. 

We  may  conceive  the  body  as  immersed  in  a  world  full  of 
energy  manifestations  of  diverse  sorts,  but  more  or  less  com- 
pletely insulated  from  the  play  of  these  cosmic  forces  by  an 
impervious  cuticle.  The  bodily  surface,  however,  is  permeable 
in  some  places  to  these  environing  forces  and  in  a  differential 
fashion,  one  part  responding  to  a  particular  series  of  vibrations, 
another  part  to  a  different  series,  much  as  the  strings  of  a  piano 
when  the  dampers  are  hfted  will  vibrate  sympathetically  each 
to  its  own  tone  when  a  musical  production  is  played  on  a 
neighboring  instrument.  The  sense  organs,  again,  may  be 
compared  with  windows,  each  of  which  opens  out  into  a 
particular  field  so  as  to  admit  its  own  special  series  of  environ- 
mental forces.  In  each  species  of  animals  these  windows  are 
arranged  in  a  characteristic  way,  so  as  to  admit  only  those 
forms  of  energy  which  are  of  practical  "significance  to  that 
animal  as  it  fives  in  its  own  natural  environment. 

The  sensory  equipment  of  the  human  race  was  thus  estab- 
lished by  the  biological  necessities  of  our  immediate  animal 
ancestors,  and  there  is  no  evidence  of  subsequent  improvement 
in  these  peripheral  physiological  mechanisms  or  of  any  increase 
in  the  number  of  our  senses  during  the  advancement  of  human 
culture.  The  advance  in  efficiency  of  the  human  race  as  com- 
pared with  its  brutish  ancestors  is  to  be  sought  rather  in  a  more 
efficient  central  apparatus  in  the  brain  for  the  utilization  of  the 
sensory  data  for  the  welfare  of  the  organism.  What  the  prog- 
ress of  science  has  accomplished  is  to  supplement  the  limited 


THE  RECEPTORS  AND  EFFECTORS  79 

sensory  equipment  of  primitive  man  by  various  indirect  means. 
To  recur  to  our  analogy  of  a  house  with  many  windows,  we 
have  not  been  able  to  increase  the  number  of  windows  so  as 
to  look  out  directly  into  new  fields;  but  we  have  increased  the 
range  of  vision  through  the  old  windows,  much  as  a  telescope 
brings  remote  objects  near  and  as  a  periscope  enables  the 
observer  to  see  around  a  corner.  To  the  development  of  the 
cerebral  cortex  we  owe  the  acquisition  of  these  new  powers 
which  have  opened  to  us  the  realms  of  electric  vibrations, 
ultra-violet  rays,  and  many  other  natural  phenomena  to  which 
our  unaided  sense  organs  are  quite  insensitive. 

Children  in  the  Idndergarten  are  taught  that  there  are  five 
senses.  In  reahty,  there  are  more  than  twenty  different  senses. 
Some  of  the  sense  organs  are  stimulated  by  external  objects  and 
hence  are  termed  exteroceptors;  others  are  stimulated  by  inter- 
nal excitations  of  the  visceral  organs  and  are  termed  interocep- 
tors.  Still  further  classifications  have  been  suggested,  to  which 
reference  will  be  made  shortly.  Here  we  must  first  consider 
the  criteria  in  accordance  with  which  the  various  senses  are 
distinguished. 

The  analysis  and  classification  of  the  senses  is  by  no  means 
so  simple  a  task  as  one  might  at  first  suppose.  It  is  true  that 
ordinarily  we  do  not  confuse  a  thing  seen  with  a  sound  heard; 
but,  on  the  other  hand,  we  do  constantly  confuse  savors  with 
odors,  and  it  often  requires  refined  physiological  experimenta- 
tion to  determine  whether  the  organ  of  taste  or  the  organ  of 
smell  is  the  source  of  the  sensory  excitation  in  question.  Most 
of  the  common  "flavors"  of  food  are,  in  reality,  odors  and  are 
perceived  by  the  organ  of  smell  only.  A  bad  cold  which  closes 
the  posterior  nasal  passages  makes  "all  food  taste  alike"  for 
this  reason.  In  reality,  as  we  have  already  seen,  there  are  only 
four  tastes  recognized  by  the  physiologists,  viz.,  sweet,  sour, 
salty,  and  bitter. 

Confusion  has  arisen  in  the  attempts  to  analyze  these  two 
senses  from  the  fact  that  different  physiologists  have  used 
different  definitions  of  a  "sense."  One  author,  who  defines 
these  senses  in  terms  of  the  physical  agents  which  excite  them, 
says  that  taste  is  stimulated  by  liquids  and  smell  by  vapors, 
and  that,  accordingly,  aquatic  animals,  whose  nostrils  are  filled 


80  INTRODUCTION    TO   NEUROLOGY 

with  water,  have  by  definition  no  sense  of  smell.  Other 
authors  separate  these  senses  according  to  the  organ  stimu- 
lated, the  excitation  of  the  nose  being  smell,  that  of  the  taste- 
buds  being  taste,  regardless  of  the  nature  of  the  exciting  sub- 
stance or  of  the  subjective  quality  of  the  sensation. 

There  are,  in  reality,  four  different  factors  which  must  be 
taken  into  account  in  defining  a  ''sense."  (1)  Doubtless 
with  us  human  folk  the  most  important  criterion  is  direct 
introspective  experience,  the  psychological  criterion.  Ordi- 
narily this  is  adequate,  but,  as  we  have  just  seen,  there  are 
some  cases  where  it  alone  cannot  be  depended  upon  to  dis- 
tinguish between  two  senses.  (2)  The  adequate  stimuli 
of  the  various  senses  exhibit  characteristic  physical  or  chemical 
differences,  the  physical  criterion.  This  factor,  too,  must  be 
carefully  investigated  or  we  may  be  led  astray.  (3)  The  data 
of  anatomy  and  experimental  physiology  may  differentiate 
structurally  the  receptive  organs  and  conduction  paths  of 
the  several  types  of  sensation,  the  anatomical  criterion.  (4) 
Finally,  the  type  of  response  varies  in  a  characteristic  way  for 
the  different  senses,  the  physiological  criterion. 

The  fourth  criterion  has  been  applied  to  solve  the  problem  of 
the  reason  for  the  development  of  two  very  different  types  of 
sense  organs  and  cerebral  connections  for  the  senses  of  smell  and 
taste,  both  of  which  are  chemical  senses  with  similar  subjective 
qualities.  It  has  been  pointed  out  by  Sherrington  that  taste 
is  an  interoceptive  sense,  calling  forth  visceral  responses  within 
the  body,  while  smell  is,  in  part  at  least,  an  exteroceptive 
sense,  being  excited  by  objects  at  a  distance  from  the  body  and 
calling  forth  movements  of  locomotion  carrying  the  whole 
body  toward  or  away  from  the  source  of  the  odorous  emana- 
tions. Thus  the  form  of  the  response  is  here  the  distinctive 
factor,  and  incidental  to  this  feature  the  organs  of  smell  are 
sensitive  to  far  smaller  quantities  of  the  stimulating  substance 
than  are  the  taste-buds.  Parker  and  Stabler  have  shown  that 
the  human  organ  of  smell  is  sensitive  to  alcohol  at  a  dilution 
24,000  times  greater  than  that  necessary  to  stimulate  the 
organs  of  taste  (see  p.  242) . 

it  is  impossible  in  the  present  state  of  our  knowledge  to 
frame  adequate  definitions  of  all  the  senses  in  terms  of  any 


THE  RECEPTORS  AND  EFFECTORS  81 

one  of  these  four  criteria  alone,  although  it  is  a  reasonable  hope 
that  this  may  at  some  future  time  be  attained.  Even  when  all 
of  these  criteria  are  taken  into  account,  it  is  by  no  means  easy  to 
determine  how  many  separate  senses  the  normal  human  being 
possesses.  Not  only  is  there  a  considerable  number  of  sense 
organs  not  represented  at  all  in  our  traditional  list  of  five  senses, 
but  several  of  these  five  are  complex.  Thus,  the  internal  ear 
includes  two  quite  distinct  organs — the  cochlea,  which  serves  as 
a  receptor  for  sounds,  and  the  labyrinth,  whose  semicircular 
canals  serve  as  the  chief  sense  organs  concerned  in  the  regula- 
tion of  bodily  position  and  the  maintenance  of  equilibrium, 
functions  which  are  quite  distinct  from  hearing.  The  skin, 
too,  serves  not  only  as  the  chief  organ  of  touch,  but  also  the 
additional  functions  of  response  to  warm,  cold,  and  painful 
impressions,  besides  some  other  more  obscure  sensory  activi- 
ties, such  as  tickle. 

An  acceptable  classification  of  the  sense  organs  or  receptors 
of  the  body  must  take  account  of  their  anatomical  relations,  of 
the  nature  of  the  physical  or  chemical  forces  which  serve  as  the 
adequate  stimuli,  of  the  subjective  qualities  which  we  experi- 
ence upon  their  excitation,  and  of  the  character  of  the  physio- 
logical responses  which  commonly  follow  their  stimulation. 
The  last  point  has  been  too  much  neglected. 

In  fact,  the  most  fundamental  division  of  the  nervous  sys- 
tem which  we  have,  cutting  down  through  the  entire  bodily 
organization,  is  based  upon  this  physiological  criterion.  From 
this  standpoint  we  divide  the  nervous  organs  into  two  great 
groups:  (1)  a  somatic  group  pertaining  to  the  body  in  general 
and  its  relations  with  the  outer  environment,  and  (2)  a  visceral, 
splanchnic,  or  interoceptive  group.  The  latter  group  com- 
prises the  nerves  and  nerve-centers  concerned  chiefly  with 
digestion,  respiration,  circulation,  excretion,  and  reproduction. 
These  are  intimately  related  with  the  sympathetic  nervous 
system  and  those  parts  of  the  central  nervous  system  directly 
connected  therewith,  though  the  more  highly  specialized 
members  of  this  group  are  independent  of  the  sympathetic 
system.  The  somatic  group  comprises  the  greater  part  of  the 
brain  and  spinal  cord  and  the  cranial  and  spinal  nerves,  or, 
briefly,  the  cerebro-spinal  nervous  system  as  distinguished 


§2       .       INTRODUCTION  TO  NEUROLOGY 

from  the  sympathetic  system  (see  p.  250).  This  is  the  mech- 
anism by  which  the  body  is  able  to  adjust  its  own  activities 
directly  in  relation  to  those  of  the  outside  world — to  procure 
food,  avoid  enemies,  and  engage  in  the  pursuit  of  happiness. 

The  organs  belonging  to  each  of  these  two  groups  do  much  of 
their  work  independently  of  the  other  group,  i.  e.,  visceral 
stimuli  call  forth  visceral  responses  and  external  or  somatic 
stimuli  call  forth  somatic  responses.  Nevertheless,  the  two 
groups  of  organs  are  by  no  means  entirely  independent,  for 
external  excitations  may  produce  strong  visceral  reactions, 
and  conversely.  Thus,  the  sight  of  luscious  fruit  (extero- 
ceptive stimulus)  naturally  calls  forth  movements  of  the  body 
(somatic  responses)  to  go  to  the  desired  object  and  seize  it. 
But  if  one  is  hungry,  the  mouth  may  water  in  anticipation, 
a  purely  visceral  response.  On  the  other  hand,  the  strictly 
visceral  (interoceptive)  sensation  of  hunger  is  apt  to  set  in 
motion  the  exteroceptive  reactions  necessary  to  find  a  dinner. 

Sherrington,  whose  analysis  with  some  modifications  is  here 
adopted,  recognizes  three  types  of  sense  organs  or  receptors: 
(1)  the  interoceptors,  or  visceral  receptive  organs,  which  respond 
only  to  stimulation  arising  within  the  body,  chiefly  in  connec- 
tion with  the  processes  of  nutrition,  excretion,  etc.;  (2)  the 
exteroceptors,  or  somatic  sense  organs,  which  respond  to  stim- 
ulation arising  from  objects  outside  the  body;  (3)  the  pro- 
prioceptors, a  system  of  sense  organs  found  in  the  muscles, 
tendons,  joints,  etc.,  to  regulate  the  movements  called  forth 
by  the  stimulation  of  the  exteroceptors.  This  third  group 
is  really  subsidiary  to  the  somatic  group,  or  exteroceptors, 
and  will  be  considered  more  in  detail  below. 

The  proprioceptive  sense  organs  are  deeply  embedded  in  the 
tissues  and  are  typically  excited  by  those  activities  of  the  body 
itself  which  arise  in  response  to  external  stimulation.  The 
proprioceptors  then  excite  to  reaction  the  same  organs  of  re- 
sponse as  the  exteroceptors  and  regulate  their  action  by  rein- 
forcement or  by  compensation  or  by  the  maintenance  of 
muscular  tone.  All  reactions  concerned  with  motor  coordi- 
nation, with  maintenance  of  posture  or  attitude  of  the  body, 
and  with  equilibrium  involve  the  proprioceptive  system. 

The  distinction  between  somatic  and  visceral  systems  of  organs  and 


THE  RECEPTORS  AND  EFFECTORS  83 

nerves  is  variously  drawn  by  different  neurologists  depending  upon 
whether  anatomical,  embryological  or  physiological  criteria  are  given 
greater  weight.  According  to  the  usage  here  adopted,  somatic  organs 
and  nerves  are,  in  general,  concerned  with  responses  to  external  stimu- 
lation in  which  the  body  or  its  members  are  oriented  with  reference  to 
these  stimuli,  the  response  being  excited  through  the  exteroceptors  and 
the  course  of  the  reaction  controlled  through  the  proprioceptors.  Vis- 
ceral organs  and  nerves,  on  the  other  hand,  are  concerned  with  re- 
sponses to  internal  stimulation  through  the  interoceptors  which  involve 
no  spatial  orientation  of  the  body. 

The  nerves  of  proprioceptive  sensibility  were  first  experimentally 
demonstrated  and  their  significance  clearly  explained  by  Sir  Charles 
Bell  more  than  a  century  ago  (see  the  references  cited  on  p.  158). 

The  important  point  to  bear  in  mind  here  is  that  stimulation 
of  the  visceral  sense  organs  typically  calls  forth  visceral 
responses,  i.  e.,  adjustments  wholly  within  the  body,  while 
stimulation  of  the  somatic  sense  organs  typically  calls  forth 
somatic  responses,  i.  e.,  a  readjustment  of  the  body  as  a  whole 
with  reference  to  its  environment.  This  a  very  fundamental 
distinction.  These  two  functions  are  quite'  diverse  and  the 
organization  of  these  two  parts  of  the  nervous  system  shows 
corresponding   structural   differences. 

The  internal  adjustments  of  the  visceral  systems  are  effected 
by  a  nicely  balanced  mechanism  of  local  and  general  reflexes  so 
arranged  that  most  of  their  work  is  done  quite  mechanically 
and  unconsciously.  The  taking  of  food  and  its  preliminary 
mastication  are  generally  voluntary  acts  whose  various  proc- 
esses' are — or  may  be — controlled  at  will.  But  once  the  food 
has  passed  into  the  esophagus,  the  further  work  of  swallow- 
ing, digestion,  and  assimilation  is  no  longer  under  direct  con- 
trol. The  presence  of  a  morsel  of  food  in  the  upper  part  of 
the  esophagus  excites  the  muscular  movements  necessary 
for  the  completion  of  the  act  of  swallowing,  which  no  act  of 
will  can  prevent  or  modify.  In  fact,  any  attempt  at  conscious 
interference  or  regulation  is  apt  to  result  in  an  incoordination 
of  the  movements  involved,  and  sputtering  or  gagging  may 
result. 

The  mechanisms  involved  in  these  processes  are  inborn  and 
require  no  practice  for  their  perfect  performance.  They  are 
innate,  invariable,  and  essentially  similar  in  all  members  of  a 
race  or  species.  They  are,  moreover,  nicely  adapted  to  the 
mode  of  life  characteristic  of"  the  species.     In  a  carnivorous 


84  INTRODUCTION  TO  NEUROLOGY 

animal  the  whole  physiological  machinery  of  nutrition  is 
different  from  that  of  a  herbivorous  animal.  These  physio- 
logical and  structural  peculiarities  by  which  each  species  of 
animal  is  adapted  to  its  mode  of  life  have  been  brought  about 
by  natural  selection  and  other  evolutionary  factors.  This  is 
not  absolutely  true  of  all  visceral  actions;  some  are  acquired 
and  modifiable.     But  as  a  general  rule  this  is  their  type. 

Some  of  the  somatic  actions  are  likewise  innate  and  relatively 
fixed  in  character.  This  is  true  of  most  of  the  proprioceptive 
reactions  and  of  many  of  the  exteroceptive  as  well.  Fish  can 
swim  as  soon  as  they  are  hatched;  chicks  just  out  of  the  shell 
have  an  instinctive  tendency  to  peck  at  all  small  objects  on 
the*  ground.  But  in  most  of  these  cases  (of  which  innumerable 
instances  might  be  cited)  some  practice  is  necessary  before 
perfect  responses  are  attained;  and  a  very  large  proportion 
of  the  exteroceptive  acts  are  not  innate,  but  acquired  by  long 
and  often  arduous  experience.  In  higher  vertebrates,  as  a 
rule,  all  but  the  simplest  and  most  elementary  exteroceptive 
activities  are  individually  acquired,  variable,  non-hereditary, 
plastic  behavior  types.  The  elements  of  which  these  acts 
are  made  up  are,  of  course,  necessarily  present  in  the  inherited 
reflex  pattern;  but  the  pattern  according  to  which  these  ele- 
ments are  combined  is  not  wholly  predetermined  in  the 
hereditary  organization  of  the  species  (pp.  32,  335). 

With  these  principles  in  mind,  let  us  now  undertake  an  analy- 
sis of  the  human  receptors  and  of  the  nervous  end-organs  re- 
lated to  their  effectors,  or  organs  of  response.  The  following 
Hst  is  by  no  means  complete  and  is  in  some  parts  merely 
provisional. 

I.  SOMATIC  RECEPTORS 

These  are  concerned  with  the  adjustment  of  the  body  to  external  or 
environmental  relations. 

A.   The  Exteroceptive  Group 

The  sense  organs  of  this  group  are  stimulated  by  objects  outside  the 
body  and  typically  call  forth  reactions  of  the  whole  body,  such  as  locomo- 
tion, or  of  its  parts,  so  as  to  change  the  relation  of  the  body  to  its  environ- 
ment. This  group  includes  a  system  of  general  cutaneous  sense  organs, 
some  organs  of  deep  sensibility,  and  some  of  the  higher  sense  organs. 
The  cutaneous  exteroceptors  comprise  a  very  complex  system  whose 


THE  RECEPTORS  AND  EFFECTORS 


85 


analysis  has  proved  very  difficult.  The  correlation  of  the  data  of  physi- 
ological experiment  with  the  anatomical  structure  of  the  cutaneous 
end-organs  is  still  somewhat  problematical  and  the  assignment  of  end- 
organs  here  to  the  various  cutaneous  senses  should  be  regarded  as  provi- 
sional rather  than  as  demonstrated. 

1.  Organs  of  Touch  and  Pressure. — These  fall  into  two  groups,  those 
for  deep  sensibility  (pressure)  and  those  for  cutaneous  sensibility  (touch). 

The  deep  pressure  sense  is  served  by  nerve-endings  throughout  the 
tissues  of  the  body  and  is  preserved  intact  after  the  loss  of  all  cutaneous 
nerves.     Most  of  the  functions  of  the  deep  senisory  nerves  belong  to  the 


Fig.   22. — Pacinian  corpuscles  from  the  peritoneum  of  a  cat. 
from  Bohm-Davidoff-Huber's  Histology.) 


(After  Sala, 


proprioceptive  and  interoceptive  series  (see  below),  but  some  extero- 
ceptive functions  are  here  present  also.  The  latter  are  probably  re- 
lated chiefly  to  the  Pacinian  corpuscles  and  similar  encapsulated  end- 
organs.  The  Pacinian  corpuscle  has  a  central  nerve-fiber  enclosed  in  a 
firm  lamellated  connective-tissue  sheath  (Fig.  22).  Bj'-  these  end-or- 
gans relatively  coarse  pressure  may  be  discriminated  and  localized 
(exteroceptive  function),  and  movements  of  muscles  and  joints  can  be 
recognized  (proprioceptive  function).  The  sensory  fibers  concerned  with 
the  deep  pressure-sense  are  distributed  through  the  muscular  branches 
of  the  spinal  nerves  in  company  with  the  motor  fibers.  The  point 
stimulated  can  be  localized  with  a  fair  degree  of  accuracy. 


86 


INTRODUCTION    TO    NEUROLOGY 


The  cutaneous  organs  of  tactile  sensibility  are  of  several  kinds,  whose 
precise  functions  are  still  obscure.  There  are  two  principal  groups  of 
these  those  arranged  in  the  hair  bulbs  at  the  roots  of  the  hairs  and 
those  on  the  hairless  parts,  such  as  the  lips,  the  palms  of  the  hands,  and 
the  soles  of  the  feet.  The  latter  are  more  highly  differentiated  endings 
and  are  organs  of  the  most  refined  active  touch. 

Most  of  the  surface  of  the  body  is  more  or  less  hairy,  though  many  of 
these  hairs  may  be  so  fine  as  to  escape  observation.     The  hairs  are  the 


K^k^.. 


,. &i 


mm 


Fig.  23. — Nerve-endings  about  a  large  hair  from  the  dog.  The  nerve- 
fibers  are  shown  in  black  surrounding  the  hair  shaft,  the  straight  fibers 
at  b  and  the  circular  fibers  at  c.  (After  Bonnet,  from  Barker's  Nervous 
System.) 

most  important  sources  of  excitation  of  the  first  group  of  cutaneous  sense 
organs,  and  the  sensitiveness  of  the  hair-clad  parts  is  greatly  reduced 
after  the  hair  is  shaved.  The  threshold  of  excitation  to  touch  of  the  skin 
about  the  base  of  a  hair  is  from  three  to  twelve  times  higher  than  that  of 
a  similar  excitation  applied  to  the  hair  itself.  The  innervation  of  the 
hair  bulbs  is  very  complex  and  varies  greatly  for  different  animals  and 
for  the  different  kinds  of  hairs  on  the  same  body,  so  that  no  general 
description  is  possible. 


THE  RECEPTORS  AND  EFFECTORS 


87 


Miss  Vincent  has  shown  that  the  large  vibrissee  of  the  rat  receive  their 
nerve-supply  from  two  sources.  A  large  nerve  bundle  pierces  the  deep 
layer  of  tlie  skin  (dermis)  in  the  lower  part  of  tlie  hair  bulb,  spreads  out 
over  the  inner  hair  folhule  in  a  heavy  plexus,  and  terminates  chiefly  in  a 
mantle  of  touch  cells,  resembling  Merkel's  corpuscles  (see  Fig.  26),  in  the 
outer  root  sheath  all  over  the  follicle.  A  second  nerve  supply  comes  from 
the  dermal  plexus  of  the  skin,  from  which  branches  run  clown  and  form  a 
nerve  ring  about  the  neck  of  the  follicle.     Experimental  studies  show  that 


stratum  lucidum 

Stratum 

granulosum 


Fig.  24. — Section  through  the  human  skin,  illustrating  the  five  layers 
of  the  epidermis  and  the  papillse  of  the  dermis  or  corium.  A  corpuscle  of 
Meissner  is  seen  within  one  of  the  dermal  papillae.  (From  Cunningham's 
Anatomy.) 


these  hairs  are  very  important  not  only  as  general  tactile  organs,  but 
specifically  as  aids  in  locomotion  and  equilibration.  The  ordinary  hairs 
of  man  and  other  mammals  have  three  forms  of  specific  nerve-endmgs  in 
addition  to  various  forms  of  terminal  arborizations  in  the  surrounding 
tissues:  (1)  straight  and  often  forked  endings  running  parallel  with  the 
base  of  the  hair;  (2)  circular  fibers  forming  a  plexiform  ring  around  the 
root  of  the  hair  external  to  the  straight  endings;  and  (3)  leaf -like  nerve- 


88  INTRODUCTION   TO    NEUROLOGY 

endings  associated  with  special  cells  resembling   Merkel's  corpuscles. 
Figure  23  illustrates  the  first  and  second  types  of  these  endings. 

Under  the  hairless  parts  of  the  skin  there  are  special  tactile  bodies,  such 
as  Meissner's  corpuscles.  These  are  generally  found  in  the  deep  layer  of 
the  skin  (dermis)  and  in  the  underlying  tissues,  either  as  free  skein-like 
terminal  aborizations  of  cutaneous  nerves  or  as  similar  more  elaborate 
endings  enclosed  in  connective-tissue  capsules.  Figures  24  and  25  illus- 
trate the  most  highly  differentiated  form  of  these  endings,  the  Meissner 
corpuscles.  Merkel's  corpuscles  (Fig.^  26),  which  are  found  in  the  epi- 
dermis and  elsewhere,  are  probably  simpler  organs  of  this  system. 


Fig.  25. — The  details  of  the  nerve-endings  in  a  Meissner  corpuscle  from 
the  human  skin.  Only  the  outline  of  the  corpuscle  is  shown,  within  which 
the  terminals  of  the  nerve-fiber  form  a  complex  skein.  (After  Dogiel,  from 
Bohm-Davidoff-Huber's  Histology.) 

All  forms  of  cutaneous  sensibility  (touch,  temperature,  and  pain)  when 
studied  physiologically  are  found  to  be  localized  in  small  areas  or  sensory 
spots,  each  of  which  has  a  specific  sensibility  to  one  only  of  the  cutaneous 
sensory  qualities.  The  intervening  parts  of  the  skin  are  insensitive.  An 
immense  amount  of  physiological  and  clinical  observation  has  been  de- 
voted to  the  analysis  of  cutaneous  sensibility,  including  the  experimental 
division  of  cutaneous  nerves  in  their  own  bodies  by  Head,  Trotter  and 
Davies,  and  Boring  for  the  purpose  of  studying  more  critically  the  dis- 
tribution of  the  various  sensory  functions  in  and  round  the  anesthetic 


THE  RECEPTORS  AND  EFFECTORS  89 

areas  produced  by  the  injuries  and  the  phenomena  accompanying  the 
restoration  of  these  functions  during  tlie  regeneration  of  the  nerves. 
But  general  agreement  has  not  yet  been  reached  on  all  questions. 

Head  and  his  colleagues  are  of  the  opinion  that  all  forms  of  cutaneous 
sensibiUty  (touch,  temperature,  and  pain)  are  grouped  in  two  series,  each 


Fig.  26. — Merkel's  corpuscles  or  tactile  disks  from  the  skin  of  the  pig's 
snout.  The  nerve-fiber,  ri,  branches,  and  each  division  ends  in  an  expanded 
disk,  m,  which  is  attached  to  a  modified  cell  of  the  epidermis,  a.  The  un- 
modified cells  of  the  epidermis  are  shown  at  c.      (From  Ranvier.) 

served  by  different  nerve-fibers  and  end-organs;  these  he  terms  "proto- 
pathic"  and  "epicritic"  sensibility.  Protopathic  sensibility  is  subjec- 
tively general  diffuse  sensibility  of  a  primitive  form.  Its  sense  organs  are 
arranged  in  definite  spots,  and  yet  these  sensations  have  no  clear  local 
reference  or  sign;  that  is,  the  spot  stimulated  cannot  be  accurately  lo- 
calized.    There  are  separate  spots  for  touch,  heat,  cold,  and  pain ;  these 


Fig.  27. — End-bulb  of  Krause  from  the  conjunctiva  of  man.  The  nerve- 
ending  forms  a  globular  skein  within  a  delicate  connective-tissue  capsule. 
(After  Dogiel.) 

spots  being  generallj^  grouped  near  the  haii*  bulbs.  In  fact,  the  hairs  are 
the  most  important  tactile  organs  of  this  system  and  the  other  sense 
qualities  belonging  here  are  intimately  associated  with  the  roots  of  the 
hairs.  Epicritic  sens'ibility  is  a  more  refijied  sort  of  discrimination  and 
is  regarded  as  a  later  evolutionary  type.     It  includes  light  touch,  on  the 


90 


INTRODUCTION   TO    NEUROLOGY 


hairless  parts  of  the  body  particularly,  and  the  discrimination  of  the 
intermediate  degrees  of  temperature.  Cutaneous  localization  and  the 
discrimination  of  the  distance  between  two  points  simultaneously  stimu- 
lated (the  "compass  test")  are  functions  of  this  system;  but  pain  sensi- 
biUty  is  not  included,  this  being  wholly  protopathic. 

Trotter  and  Davies  repeated  some  of  Head's  experiments  and,  while 
confirming  most  of  his  observations,  they  were  led  to  somewhat  different 
conclusions.  They  do  not  regard  the  protopathic  and  epicritic  series  as 
served  by  distinct  systems  of  nerves,  but  as 
different  physiological  phases  of  the  same 
systems  of  nerve-fibers  and  end-organs.  Carr 
subjected  Head's  own  data  to  critical  analysis 
and  concluded  that  these  data  do  not  support 
the  distinction  between  the  protopathic  and 
epicritic  types  of  sensibility.  Boring  repeated 
Head's  experimental  division  of  a  cutaneous 
nerve  in  his  own  body  with  far  more  precise 
methods  of  study,  and  he  also  concluded  that 
the  protopathic  and  epicritic  groups  of  sensa- 
tions do  not  exist.  It  may  be  concluded,  there- 
fore, that  this  distinction  may  hereafter  be  ig- 
nored. Boring  further  found  that  two-point 
discrimination  (compass  test)  is  effected  by 
the  deep  rather  than  by  the  cutaneous  nerves, 
as  Head  supposed  (see  p.  195). 

2.  End-organs  for  Sensibility  to  Cold. 

3.  End-organs  for  Sensibility  to  Heat. — 
Physiological  experiment  shows  that  warmth 
and  cold  are  sensed  by  different  parts  of  the 
skin  (the  warm  spots  and  the  cold  spots  re- 
spectively), and  Head  is  of  the  opinion  that 
each  of  these  types  of  sensibility  may  be  present 
in  an  epicritic  and  a  protopathic  form.  What 
end-organs  are  involved  here  is  by  no  means 
certain.  The  margin  of  the  cornea  was  found 
by  von  Frey  to  be  sensitive  to  pain  and  cold 
only.  The  free  nerve-endings  found  here  he 
assumes  to  be  pain  receptors  and  the  end- 
bulbs  of  Krause  (Fig.  27)  to  be  cold  receptors. 
By  an  analogous  argument  he  assumes  that 
the  "genital  corpuscles"  of  Dogiel  and  some 
similar  endings  widely  distributed  in  the  skin 
are  warmth  receptors.  By  some  other  physi- 
ologists these  types  of  corpuscles  are  regarded 
as  belonging  to  the  tactile  system .    Stimulation 

of  the  somatic  nerves  of  deep  sensibility  causes  no  temperature  sensa- 
tions.    (For  temperature  sensations  in  the  viscera  see  p.  269.) 

4.  End-organs  for  Pain. — Some  physiologists  believe  that  there  are 
separate  nerve-endings  for  pain;  others  regard  pain  as  a  quality  which 
may  be  present  in  any  sense,  and  not  as  itself  a  true  sensation  (pp.  277ff.). 
The  free  nerve-endings  among  the  cells  of  the  epidermis  are  regarded  by 
von  Frey  as  the  pain  receptors,  because  these  endings  alone  are  present 
in  some  parts  of  the  body  where  susceptibility  to  pain  is  the  only  sense 


^    .,--71 

Fig.  28. — Longitudinal 
section  of  a  tooth  of  a 
fish,  Gobius,  showing 
nerve  terminals:  d,  den- 
tin; n,  nerve-fibers  enter- 
ing the  cavity  of  the  den- 
tin and  ending  free. 
(After  Retzius,  from  Bar- 
ker's Nervous  System.) 


THE  RECEPTORS  AND  EFFECTORS 


91 


quality  present,  such  as  the  dentin  and  pulp  of  the  teeth  (Fig.  28),  the 
cornea,  and  the  tympanic  nienibrane  of  the  ear  (J.  G.  Wilson). 

Similar  endinj^s  are  found  throughout  the  epidermis  (Fig.  29)  and  in 
many  deep  structures.  Tlie  nerves  of  deep  sensibility  of  the  somatic 
sensory  type  may  also  carrj'  painful  impressions.  (For  visceral  pain  see 
pp.  270,  278.)  According  to  Head,  cutaneous  pain  is  wholly  of  proto- 
pathic  type,  and  in  case  of  injury  to  the  peripheral  nerves  it  disappears 
and  reappears  in  regeneration  simultaneously  with  the  protopathic  type 
of  tactile  and  temperature  sensation.  This  cutaneous  pain  is  not  ac- 
curately localizable  unless  epicritic  cutaneous  sensibility  is  also  present. 


Fig.  29. — Transverse  section  through  the  skin  of  the  ear  of  a  white  mouse. 
The  dotted  line  marks  the  lower  border  of  the  epidermis:  a,  horizontal 
nerve-fibers;  b,  bifurcation  of  nerve-fibers ; /«,  cutaneous  nerve-fibers.  (After 
Van  Gehuchten,  from  Barker's  Nervous  System.) 


5.  End-organs  of  General  Chemical  Sensibility. — In  man  this  type  of 
sensibiUty  is  found  only  on  moist  epithelial  surfaces,  such  as  the  mouth 
cavity ;  but  in  fishes  it  may  be  present  over  the  entire  surface  of  the  body. 
The  sense  organ  is  probably  the  free  nerve  terminals  among  the  cells  of 
the  epithelium,  never  special  sense  organs  like  taste-buds,  for  these  when 
present  in  the  skin  belong  to  a  quite  different  system.  Coghill  has 
recently  shown  that  the  supposed  sensitivity  of  the  amphibian  skin  to 
acids  is  really  due  to  a  destructive  action  of  the  reagents  upon  the  epithe- 
lium; but  Crozier  finds  evidence  for  true  chemical  sensibility  in  the  skin, 
and  the  entire  question  of  diffuse  chemical  sensibility  requires  further 
studv. 


92 


INTRODUCTION    TO    NEUROLOGY 


6.  Organs  of  Hearing. — The  stimulus  is  material  vibrations  whose 
frequency  ranges  from  30  to  30,000  per  second  (see  p.  75).  The  receptor 
is  the  spiral  organ  (organ  of  Corti)  in  the  cochlea  of  the  ear  (see  p.  219), 
and  perhaps  also  the  sensory  spots  in  the  saccule  and  utricle.  There  are 
two  forms  of  auditory  sensations:  (1)  noise,  stimulated  by  sound  con- 
cussions or  irregular  mixtures  of  aerial  vibrations;  (2)  tone,  stimulated 
by  sound  waves  or  periodic  aerial  vibrations. 

7.  Organs  of  Vision. — The  stimulus  is  ethereal  vibrations  ranging  be- 
tween 400,000  billions  and  800,000  billions  per  second.  Here  also  there 
are  two  forms:  (1)  brightness,  stimulated  by  mixed  ethereal  vibrations; 
(2)  color,  stimulated  by  simpler  ethereal  vibrations.  (On  the  structure 
of  the  eye  and  its  connections  see  p.  228.) 

8.  Organs  of  Smell. — This  sense  has  both  exteroceptive  and  intero- 
ceptive qualities,  the  latter  being  apparently  the  more  primitive.  (See 
pp.  80,  97,  and  242.) 

B.  The  Proprioceptive  Group 

These  sense  organs  are  contained  within  the  skeletal  muscles,  joints, 
etc.,  and  are  stimulated  by  the  normal  functioning  of  these  organs,  thus 
reporting  back  to  the  central  nervous  system  the  exact  state  of  contrac- 
tion of  the  muscle,  flexion  of  the  joint,  and  tension  of  the  tendon.  Cu- 
taneous sensibility  may  also  participate  in  these  reactions,  which  are 
generally  unconsciously  performed. 


Fig.  30. — Muscle  spindle  from  the  muscles  of  the  foot  of  a  dog.  Three 
muscle-fibers  are  shown  and  three  sensory  nerve-fibers,  which  enter  the 
muscle  spindle,  branch,  and  wind  spirally  around  the  muscle-fibers  (a,  b). 
A  sympathetic  nerve-fiber  (Sy.n.)  also  enters  the  muscle  spindle.  (After 
Huber  and  DeWitt,  from  Barker's  Nervous  System.) 

9.  End-organs  of  Muscular  Sensibility. — The  organ  is  a  series  of 
nerve-endings  among  special  groups  of  muscle-fibers  known  as  muscle 
spindles.  These  endings  are  usually  spirally  wound  around  their  muscle- 
fibers  and  are  stimulated  by  the  contraction  of  the  muscle  (Fig.  30). 

As  we  shall  see  below  (p.  98),  the  muscles  are  classified  for  our  purposes 
into  three  groups:  (1)  somatic  muscles  (the  striated  skeletal  muscles);  (2) 
general  visceral  muscles  (generally  unsti'iated  and  involuntary);  and  (3) 
special  visceral  muscles  of  the  head  which  are  striated  and  voluntary. 
The  first  and  third  of  these  groups  receive  their  motor  innervation  from 


THE  RECEPTORS  AND  EFFECTORS 


93 


cerebro-spinal  nerves;  the  second,  from  sympathetic  nerves.  Tlic 
classification  of  the  nerves  of  muscle  sense  related  respectively  to  the,s(! 
three  groups  of  muscle  offers  some  difficulties.  The  striated  muscles  of 
the  first  and  third  groups  are  phj^siologically  similar  in  that  tliey  act  in 
general  in  response  to  exteroceptive  stimuli  and  thej'  nisiy  be  voluntarih- 
excited,  while  the  visceral  muscles  of  the  second  group  are  generally 
stimulated  by  interoceptive  stimuli  and  their  functions  are  usually  in- 
voluntary. I  have,  accordingly^,  somewhat  arbitrarily  regarded  the 
sensory  neives  of  the  first  and  third  groups  of  muscles  as  proprioceptors 
and  those  of  the  second  group  as  interoceptors. 

10.  End-organs  of  Tendon  Sensibility. — Nerve-endings  are  spread 
otit  over  the  surface  of  tendons  and  are  stimulated  by  stretching  the 
tendon  during  muscular  contraction  (Fig.  31). 

11.  End-organs  of  Joint  Sensibility. — Nerve-endings  found  in  the 
joints  and  the  surrounding  tissues  are  stimulated  by  bending  the  joint, 


Fig.  31. — A  teased  preparation  of  a  tendon  of  a  small  muscle  from  a 
rabbit,  showing  the  endings  of  the  nerve-fibers  of  tendon  sensibility,  each 
of  which  spreads  out  widely  over  the  surface  of  the  tendon.  (After  Huber 
and  DeWitt,  from  the  Journal  of  Comparative  Neurology.) 

and  report  back  to  the  central  nervous  sj^stem  the  degree  of  flexion  of  the 
joint.  The  chief  end-organs  are  probably  Pacinian  corpuscles  (see 
Fig.  22). 

12.  Organs  of  static  and  equilibratory  sensation  arising  from  stimula- 
tion of  the  semicircular  canals  of  the  internal  ear  (Fig.  32).  This  is 
the  most  highly  specialized  member  of  the  proprioceptive  group  and  acts 
in  conjunction  with  all  of  the  other  somatic  senses  to  maintain  equilibrium, 
posture,  and  the  tone  of  the  muscular  system  (see  p.  201).  The  eyes  and 
most  of  the  other  exteroceptive  sense  organs,  so  far  as  the}'  act  in  the  way 
just  suggested,  also  serve  as  proprioceptors. 


II.  VISCERAL  RECEPTORS 

The  visceral  or  interoceptive  senses  fall  into  two  well-defined  groups: 
First,  the  general  visceral  systems  are  without  highly  specialized  end- 
oi'gans  and  are  innervated  through  the  sympathetic  nervous  system. 
Their  reactions  are  chiefly  unconsciously  performed.  Second,  the  special 
visceral  senses  are  provided  with  highly  developed  end-organs  wliich  are 
innervated  directh'  from  the  brain  without  any  connection  with  the  sym- 
pathetic nervous  system.  The  special  visceral  sense  organs  may  in  some 
cases  ser%'e  as  exteroceptors  as  well  as  interoceptors.  Their  reactions 
may  be  conscious  and  voluntary. 


94 


INTRODUCTION    TO    NEUROLOGY 
A.  General,  Visceral  Group 


Many  of  the  sensations  of  this  group  are  obscure  and  a  number  of 
excito-motor  and  excito-glandular  reactions  may  be  included  here  which 


Fig.  32. — Diagram  of  the  relations  of  a  fiber  of  the  vestibular  branch 
of  the  auditory  nerve  and  its  mode  of  termination  in  the  semicircular  canal: 
CO,  the  central  nervous  system; /z,  non-nervous  supporting  cell  of  the  semi- 
circular canal;  hz,  hair  cell,  one  of  the  receptor  cells  of  the  sensory  surface; 
sn,  axon  of  the  vestibular  neuron;  sz,  cell  body  of  the  vestibular  neuron. 
(After  Retzius,  from  Barker's  Nervous  System.) 

never  come  into  clear  consciousness,  particularly  those  concerned  with 
nutrition,  excretion,  and  vasomotor  adjustments.     The  number  of  these 


THE  RECEPTORS  AND  EFFECTORS 


95 


reactions  might  be  consiilerably  increased;  for  further  discussion  of  these 
reflexes  see  p.  201. 

13.  Organs  of  Hunger. — The  stimulus  is  strong  periodic  contractions 
of  the  muscles  of  the  stomach.  Hunger  is  apparently  a  variety  of  muscle 
sense,  but  other  factors  are  also  present  i^see  p.  268). 

14.  Organs  of  Thirst. — The  specific  stimulus  here  is  probably  a  drying 
of  the  pharyngeal  mucous  membrane,  together  with  more  general 
conditions. 

15.  Organs  of  Nausea. — The  stimulus  is  probably  an  antiperistaltic 
reflex  in  the  digestive  tract  (see  p.  270). 

16.  Organs  giving  rise  to  respiratory  sensations,  suffocation,  etc.  (see 
p.  2631. 

17.  Organs  giving  rise  to  circulatory  sensations,  flushing,  heart  panics, 
etc.  (see  p.  261). 


Fig.  33. — Free  nerve-endings  in  the  mucous  membrane  of  the  esophagus 
of  a  cat.  (After  DeWitt,  from  Wood's  Reference  Handbook  of  the  Medical 
Sciences.) 

IS.  Organs  giving  rise  to  sexual  sensations. 

19.  Organs  of  sensations  of  distention  of  cavities,  stomach,  rectum, 
bladder,  etc.     This  is  a  variety  of  muscle  sense. 

20.  Organs  of  visceral  pain  (see  pp.  270,  278). 

21.  Organs  of  obscure  abdominal  sensations  associated  with  strong 
emotions  of  fright,  anger,  affection,  etc.,  characterized  (probably  cor- 
rectly) by  the  ancients  by  such  expressions  as  "yearning  of  the  bowels," 
etc.  The  stimulus  is  probably  a  tonic  contraction  of  the  unstriped 
visceral  musculature. 

The  nerve-endings  of  the  general  visceral  receptors  are  generally  either 
simple  terminals  in  the  visceral  muscles  or  free  arborizations  in  or  under 
the  various  mucous  surfaces,  without  the  development  of  specialized 
accessoiy  cells  to  form  differentiated  sense  organs.  Figure  33  illustrates 
a  sensor\-  ending  in  the  mucous  membrane  of  the  esophagus,  and  Fig.  34 
types  of  nerve-endings  upon  epithelial  cells.  The  nerve-endings  in  the 
visceral  muscles  are  very  simple  (see  Figs.  37  and  38)  and  the  separation 
of  sensory-  from  motor  endings  here  has  not  been  effected. 


96 


INTRODUCTION    TO    NEUROLOGY 


B.  Special  Visceral  Group 

22.  Organs  of  Taste. — These  are  excited  by  chemical  stimulation  of 
taste-buds  on  the  tongue  and  pharynx  by  sweet,  sour,  salty,  or  bitter 


Fig.  34. — Nerve-endings  in  the  mouth  epithehum  of  the  frog:  A,  From 
sensory  papilla  of  the  tongue;  B,  cyhnder  ceUs;  C,  isolated  rod  cell;  D,  upper 
part  of  papilla;  E,  ciliate  cells  of  palate.  (After  Bethe,  from  Wood's  Refer- 
ence Handbook  of  the  Medical  Sciences.) 

substances.     In  man  this  is  a  strictly  interoceptive  sense;  but  in  some 
fishes  taste-buds  are  scattered  over  the  outer  body  surface  in  addition 


Fig.  35. — Taste-bud  from  the  side  wall  of  a  circumvallate  papilla  of  the 
tongue:  a,  Taste-pore;  b,  nerve-fibers,  some  of  which  enter  the  taste-bud 
(intragemmal  fibers),  while  others  end  freely  in  the  surrounding  epithelium 
(perigemmal  fibers).      (After  Merkel-Henle.) 

to  the  mouth  cavity,  and  thus  may  serve  as  exteroceptors  also.     The 
organ  is  a  flask-shaped  collection  of  specialized  epithelial  cells  of  two  sorts, 


THE  RECEPTORS  AND  EFFECTORS 


07 


supporting  and  specific  sensory  elements  (Fig.  35).  There  is  a  double 
innervation,  parti}-  by  perigemmal  fibers  whose  endings  surround  the 
bud,  and  parti}'  by  intragemmal  fibers  which  penetrate  the  bud  and 
arborize  in  intimate  relation  with  the  specific  sensory  cells. 

23.  Organs  of  Smell. — These  are  excited  by  chemical  stimulation  of 
the  specific  olfactor}-  mucous  membrane  of  the  nose.  The  number  of 
substances  which  ma}''  act  as  stimuli  is  greater  than  in  the  case  of  taste- 
buds,  the  number  of  sul^jective  qualities  is  also  greater,  and  the  discrimina- 
tion threshold  is  much  lower  (see  pp.  80  and  242).  The  peripheral  organ 
of  smell  is  a  specific  sensor}^  epithelium  within  the  nose.  The  olfactory 
epithelium  is  composed  of  non-nervous  supporting  cells  and  among  these 
the  smaller  specific  olfactory  cells.     Both  kinds  of  cells  extend  through- 


^»4^t 


Olfactory  vesicles 
—   Limiting  membrane 


Fig.  36. — Diagrams  illustrating  the  structure  of  the  olfactory  mucous 
membrane  of  the  kitten.  A,  Cross-section.  B,  A  section  taken  tangential 
to  the  surface  of  the  epithelium,  through  the  olfactorj'  limiting  membrane 
and  showing  the  rounded  openings  through  which  the  slender  olfactory  cells 
project.  The  star-shaped  structures  around  the  margin  of  this  figure  are 
ciliated  olfactory  vesicles  as  seen  when  looking  downward  upon  the  surface 
of  the  epithelium  at  a  higher  level  than  the  central  part  of  the  figure.  Drawn 
by  Dr.  O.  Van  der  Stricht;  for  fuller  description  of  these  structures,  see  his 
paper  (1909)  cited  in  the  appended  bibliography. 


out  the  entire  thickness  of  the  sensory  epithelium  (Fig.  36,  A)  and  the 
olfactory  cells  are  prolonged  at  the  base  to  form  the  fibers  of  the  olfac- 
tory nerve  (Fig.  104,  p.  242).  This  is  the  only  peripheral  nerve  in  the 
human  body  whose  fibers  arise  in  this  way  from  peripherally  placed 
cell  bodies. 

The  olfactory  cells  are  commonly  described  as  bearing  a  tuft  of  cilia  at 
their  free  ends.  The  more  precise  studies  of  Van  der  Stricht  have  shown 
that  the  olfactory  cells  project  through  openings  in  the  olfactory  limiting 
membrane  (which  is  thus  a  true  fenestrated  membrane)  and  there  expand 
into  olfactory  vesicles,  from  which  in  turn  the  olfactory  cilia  arise  (Fig. 
36).  The  ciliated  olfactor}^  vesicles  are  the  true  receptors  of  the  sense 
of  smell  and  embryologicall}'  the}'  are  derived  from  the  centrosome  and 
its  surrounding  centrosphere.  The  olfactory  vesicles  are  embedded  in 
7 


98  INTRODUCTION  TO  NEUROLOGY 

and  supported  by  an  outer  semi-fluid  cuticle  (not  shown  in  the  figure) 
secreted  by  the  supporting  cells. 

That  the  olfactory  system  was  originally  an  interoceptive  sense  seems 
clear;  but  in  all  vertebrates  living  at  the  present  time  the  visceral  re- 
sponses to  smell  are  less  important  than  the  somatic  reactions.  The 
sense  of  smell  is  the  leading  exteroceptor  in  most  lower  vertebrates,  and 
this  function  has  been  secondarily  derived  from  the  primary  visceral 
function.  We  have  seen  above  that  the  sense  of  taste  in  some  fishes  has 
secondarily  acquired  exteroceptive  functions;  and  in  the  case  of  smell  this 
secondary  change  has  been  carried  still  further  until  the  exteroceptive 
function  has  come  to  dominate  the  primitive  interoceptive,  though  the 
latter  has  by  no  means  been  entirely  obliterated. 

m.   SOMATIC   EFFECTORS 

24.  End-organs  on  Striated  Skeletal  Muscles.— This  "motor  end- 
plate"  is  a  complex  terminal  arborization  of  the  motor  nerve-fiber, 
associated  with  an  elevated  granular  mass  of  protoplasm  and  a  collection 
of  nuclei  of  the  muscle-fiber  (see  Fig.  5,  tel,  p.  41). 

The  somatic  muscles  whose  innervation  is  here  under  consideration  are 
derived  embryologically  from  the  somites,  or  primary  mesodermal  seg- 
ments of  the  embryo,  while  the  visceral  muscles  have  a  different  origin. 
They  are  under  the  direct  control  of  the  will  and  are. concerned  chiefly 
with  locomotion  or  other  movements  which  change  the  relations  of  the 
body  to  its  environment.  They  are  typically  stimulated  to  action  through 
the  exteroceptive  sense  organs.  They  make  up  the  bulk  of  the  muscula- 
ture of  the  trunk  and  limbs  and  are  represented  in  the  head  only  in  the  ex- 
ternal muscles  of  the  eyeball  and  a  part  of  the  muscles  of  the  tongue. 

rV.  VISCERAL  EFFECTORS 

25.  End-organs  on  the  Involuntary  Visceral  Muscles. — These  muscles 
may  be  unstriated  or  striated  (as  in  heart  muscle).  They  are  innervated 
through  the  sympathetic  nervous  system  and  typically  by  a  chain  of  two 
neurons,  the  preganglionic  and  the  postganglionic  neurons  (seep.  256). 
The  body  of  the  preganglionic  neuron  lies  in  the  central  nervous  sys- 
tem and  its  axon  passes  out  into  the  sympathetic  nervous  system, 
where  it  ends  in  a  sympathetic  ganglion.  The  efferent  impulse  is  here 
taken  up  by  a  post-ganghonic  neuron,  whose  body  lies  in  the  sympathetic 
ganglion  in  question  and  whose  axon  passes  onward  through  a  sympa- 
thetic nerve  to  end  in  the  appropriate  effector.  The  nerve-endings  of 
this  system  are  simple  or  branched  free  terminals  ending  on  the  surface 
of  the  muscle-fiber  (Fig.  37) ;  in  the  case  of  heart  muscle  the  fibers  usually 
have  expanded  tips  (Fig.  38). 

26.  End-organs  on  Glands. — The  innervation  of  these  organs  is  in 
most  respects  similar  to  that  of  the  involuntary  muscles  last  described. 
A  fine  plexus  of  unmyelinated  fibers  of  sympathetic  origin  envelops  the 
smaller  glands  and  pervades  the  larger  ones;  these  are  believed  in  some 
cases  to  be  the  excito-glandular  fibers. 

27.  Special  Visceral  Motor  End-organs. — The  nerves  of  these  muscles 
have  no  connection  with  the  sympathetic  nervous  system.  These  ef- 
fectors are  striated  muscles  which  may  act  under  the  direct  control  of  the 


THE  RECEPTORS  AND  EFFECTORS 


99 


will.  In  their  evolutionary  origin  they  are  derived  from  the  muscles  of 
the  gills  of  the  lower  vertebrates,  and  they  are  developed  einbryo- 
logically  from   the  ventral  unsegmented  mesoderm  and  not  from  the 


^^^^^^^M 


Fig.  37. — Two  unstriated  involuntary  muscle-fibers,  showing  the  nerve- 
endings:  a,  Axon;  b,  its  termination;  »,  nucleus  of  the  smooth  muscle  cell. 
(After  Huber  and  DeWitt,  from  Barker's  Nervous  System.) 

primitive  mesodermal  segments  which  give  rise  to  the  somatic  muscles. 
They  are  found  only  in  the  head  and  neck  and  their  nerve-endings  are 
similar  to  those  of  the  striated  muscles  of  the  somatic  series. 


'©^' 


Fig.  38. — Three    striated    cardiac    muscle    cells,    with    their    nerve-ending. 
(After  Huber  and   DeWitt,   from   Barker's   Nervous  System.) 


Summary. — We  have  seen  that  the  chief  function  of  the  sense 
organs  is  to  lower  the  threshold  of  excitabiHty  of  the  body  in 
definite  places  to  particular  kinds  of  stimulation,  and  thus  to 


100  INTRODUCTION  TO  NEUROLOGY 

effect  an  analysis  of  the  forces  of  nature  so  far  as  these  concern 
the  welfare  of  the  body.  The  nature  of  this  analysis  of  the  en- 
vironing energy  complex  was  illustrated  by  a  review  of  the 
ways  in  which  the  body  may  respond  to  different  kinds  of 
vibrations.  The  senses,  as  this  word  is  commonly  used,  were 
distinguished  by  four  criteria,  termed  briefly  the  psychologi- 
cal, physical,  anatomical,  and  physiological.  Then  followed  a 
physiological  classification  of  the  receptors  and  effectors  of  the 
human  body. 

Literature 

Barker,  L.  F.  1901.  The  Nervous  System  and  Its  Constituent 
Neurones,  New  York. 

Boring,  Edwin,  G.  1915.  The  Sensations  of  the  Alimentary  Canal, 
Am.  Jour.  Psychol.,  vol.  xxvi,  pp.  306,  ff. 

— .  1916.  Cutaneods  Sensation  after  Nerve  Division,  Quart.  Jour. 
Exper.  Physiol.,  vol.  x,  pp.  1-95. 

Carr,  Harvey.  1916.  Head's  Theory  of  Cutaneous  Sensibility, 
Psychol.  Rev.,  vol.  xxiii,  pp.  262-278. 

CoGHiLL,  G.  E.  1914.  Correlated  Anatomical  and  Physiological 
Studies  of  the  Growth  of  the  Nervous  System  of  Amphibia.  I.  The  Af- 
ferent System  of  the  Trunk  of  Amblystoma,  Jour.  Comp.  Neur.,  vol. 
xxiv,  pp.  161-233. 

Crozier,  W.  J.  1916.  Regarding  the  Existence  of  the  "Common 
Chemical  Sense"  in  Vertebrates,  Jour.  Comp.  Neur.,  vol.  xxvi,  pp.  1-8. 

VON  Frey,  M.  1897.  Untersuchungen  liber  die  Sinnesfunctionen  der 
menschlichen  Haut,  Abhangl.  kgl.  sachs.  Gesellsch.,  Bd.  40  CMath.- 
Phys.  Classe,  Bd.  23). 

Head,  H.,  Rivers,  W.  H.  R.,  and  Sherren,  J.  1905.  The  Afferent 
Nervous  System  from  a  New  Aspect,  Brain,  vol.  xxviii,  pp.  99-115. 

Herrick,  C.  Judson.  1903.  On  the  Morphological  and  Physio- 
logical Classification  of  the  Cutaneous  Sense  Organs  of  Fishes,  Amer. 
Naturalist,  vol.  xxxvii  pp.  313-318. 

— .  1908.  On  the  Phylogenetic  Differentiation  of  the  Organs  of 
Smell  and  Taste,  Jour.  Comp.  Neur.,  vol.  xviii,  pp.  157-166. 

— .  1914.  End-organs,  Nervous,  Wood's  Reference  Handbook  of  the 
Medical  Sciences,  3d  ed.,  vol.  iv,  pp.  20-27,  New  York. 

Hertz,  A.  F.  1911.  The  Sensibility  of  the  Alimentary  Canal, 
London. 

Hxjber,  G.  C.  1900.  Observations  on  Sensory  Nerve-fibers  in  Vis- 
ceral Nerves  and  on  their  Modes  of  Terminating,  Jour.  Comp.  Neur., 
vol.  x,  pp.  134-151. 

Huber,  G.  C,  and  DeWitt,  Lydia,  M.  A.  1897.  A  Contribution  on 
the  Motor  Nerve-endings  in  the  Muscle-spindles,  Jour.  Comp.  Neur., 
vol.  vii,  pp.  169-230. 

— .  1900.  A  Contribution  on  the  Nerve  Terminations  in  Neuro- 
tendinous End-organs,  Jour.  Comp.  Neur.,  vol.  x,  pp.  159-208. 

Parker,  G.  H.  1912.  The  Relation  of  Smell,  Taste,  and  the  Com- 
mon Chemical  Sense  in  Vertebrates,  Jour.  Acad.  Nat.  Sci.,  Phila.,  2  Ser., 
vol.  XV,  pp.  221-234. 


THE    RECEPTORS    AND    EFFECTORS  ]01 

Parker,  G.  H.,  and  Stabler,  Eleanor  M.  1913.  On  Certain  Dis- 
tinftions  Between  Taste  and  Smell,  Amer.  Jour.  Phv.siol.,  vol.  xxxii, 
pp.  230-240. 

Rivers,  W.  H.  R.,  and  Head,  H.  1908.  A  Human  Exi)eriment  in 
Xerve  Division,  Brain,  vol.  xxxi,  p.  323. 

Sheldon",'  R.  E.  1909.  The  Reactions  of  the  Dogfish  to  Chemical 
Stimuli,  Jour.  Comp.  Neur.,  vol.  xix,  pp.  273-311. 

Sherrington,  C.  S.  1906.  The  Integrative  Action  of  the  Nervous 
System,  New  York. 

Trotter,  W.,  and  Davies,  H.  M.  1909.  Experimental  Studies  in 
the  Innervation  of  the  Skin,  Jour,  of  Physiol.,  vol.  xxxviii,  pp.  134-246. 

Van  der  Stricht,  O.  1909.  Le  neuro-epithelium  olfactif  et  sa  mem- 
brane limitante  interne,  Mem.  Acad,  royale  de  Medecine  de  Belgique, 
tome  20,  fasc.  2. 

Vincent,  Stella  B.  1913.  The  Tactile  Hair  of  the  "WTiite  Rat, 
Jour.  Comp.  Neur.,  vol.  xxiii,  pp.  1-38. 

— .  1913a.  The  Function  of  the  Vibrissse  in  the  Behavior  of  the 
White  Rat,  Behavior  Monographs,  vol.  i,  No.  5,  pp.   7-81. 

Watson,  J.  B.  1915.  Behavior,  An  Introduction  to  Comparative 
Psychology,  Chapters  XI-XIV,  New  York. 

Wilson,  J.  G.  1911.  The  Nerves  and  Nerve-endings  in  the  Mem- 
brana  Tympani  of  Man,  Amer.  Jour.  Anat.,  vol.  xi,  pp.  101-112. 


CHAPTER  VI 
THE  GENERAL  PHYSIOLOGY  OF  THE  NERVOUS  SYSTEM 

The  functions  of  the  body  are  generally  effected  by  chemical 
changes  within  its  protoplasm.  These  chemical  changes  in  the 
aggregate  we  term  ''metabolism"  and  they  generally  involve  a 
rather  slow  interchange  of  the  chemical  substances  of  food  and 
waste  materials  between  the  cytoplasm  and  the  lymph  which 
surrounds  the  cells  and  between  the  cytoplasm  and  the  proto- 
plasm of  the  nucleus  (karyoplasm) .  The  rate  of  metabolism  is 
dependent  upon  many  factors,  one  of  which  is  the  time  required 
for  the  passage  of  soluble  substances  through  the  cell  mem- 
brane and  through  the  nuclear  membrane  which  separates  the 
cytoplasm  from  the  karyoplasm. 

In  the  nerve-cells  both  of  these  sorts  of  chemical  interchange 
are  facilitated  by  the  form  and  internal  structure  of  the  cell. 
As  we  have  already  seen  (p.  42),  the  widely  branching  dendrites 
present  a  large  surface  for  the  absorption  of  food  materials  from 
the  surrounding  lymph  and  the  elimination  of  waste.  The 
specific  nervous  functions  involve  the  consumption  of  living 
substance,  both  in  the  cell  body  and  in  the  nerve-fibers.  This 
is  in  part  an  oxidation  process,  and  this  phase  of  the  activity 
can  be  roughly  measured  by  the  amount  of  carbon  dioxid 
eliminated.  Until  very  recently  it  was  not  possible  to  secure 
any  evidence  of  CO2  production  in  nerve-fibers;  in  view  of  this 
and  of  the  further  fact  that  nerve-fibers  seem  to  be  less  sus- 
ceptible to  fatigue  than  nerve-cells  and  synapses,  many 
physiologists  assumed  that  nervous  conduction  is  not  a  chem- 
ical process,  but  perhaps  some  sort  of  molecular  vibration. 
The  conduction  of  a  nervous  impulse  through  a  living  nerve- 
fiber  is  accompanied  by  an  electric  change,  the  so-called 
negative  variation,  or  action  current,  which  by  some  physio- 
logists has  been  identified  with  the  nervous  impulse  itself. 
This  and  other  complicated  theories  of  nervous  transmission 

102 


THE    GENERAL  PHYSIOLOGY    OF   THE   NERVOUS   SYSTEM      103 

assume  that  the  process  is  essentially  a  physical  change  (prob- 
ably of  an  electric  nature)  which  involves  no  chemical  altera- 
tions, no  consumption  of  material,  no  metabolism. 

But  by  means  of  recently  devised  apparatus  of  extreme  deli- 
cacy Tashiro  has  shown  very  clearly  and  quantitatively  that 
the  resting  nerve-fiber  ehminates  CO2  and  that  during  func- 
tional activity  caused  by  stimulation  the  amount  of  CO2  is 
increased  to  about  double  that  of  the  resting  nerve.  The  same 
investigator  subsequently  showed  that  the  amount  of  COo 
given  off  by  nerve-fibers  is  quite  as  great  per  unit  of  weight  as 
that  given  off  by  the  nerve-cell  bodies  of  the  gangHa.  Tashiro 
has  shown,  moreover,  that  the  rate  of  CO2  production  is 
greater  in  that  portion  of  a  nerve-fiber  which  Hes  nearer  to  the 
source  of  the  stimulus  than  in  a  similar  portion  of  the  same 
nerve-fiber  farther  from  the  receptive  end  and  nearer  to  the 
discharging  end.  This  applies  to  both  sensory  and  motor 
fibers.  Child  has  confirmed  this  by  showing  that  different 
parts  of  the  nerve-fiber  show  differences  in  susceptibility  to 
certain  poisons  corresponding  to  the  differences  in  rate  of 
oxidation  of  their  substance.  There  is,  accordingly,  a  physio- 
logical gradient  in  the  nerve-fiber,  the  physiological  activity 
diminishing  in  the  direction  of  the  normal  conduction  of  the 
nervous  impulse.  The  neuron  is  thus  seen  to  have  an  in- 
trinsic physiological  polarity  of  its  own  quite  apart  from 
that  occasioned  by  the  irreversible  character  of  the  synapse 
(see  p.  55). 

It  is,  therefore,  probable  that  the  transmission  of  a  nervous 
impulse  involves  a  wave  of  chemical  change  throughout  the 
length  of  the  nerve-fiber,  though  a  change  of  a  quite  different 
character  from  that  occurring  in  the  cell  body  during  its  func- 
tional activity.  That  the  nervous  conduction  is  not  a  simple 
electric  discharge  through  a  free  conductor,  nor  any  other 
sort  of  simple  ethereal  or  molecular  vibratory  wave  motion,  is 
evident  from  the  fact  that  its  velocity  of  propagation  through 
the  nerve-fiber,  which  is  easilj^  measured,  is  slower  than  any 
known  wave  movement  of  this  character. 

In  the  unmyeHnated  nerves  of  vertebrates  the  rate  of  pro- 
gression of  the  nerve  impulse  varies  from  0.2  to  8  meters  per 
second;  in  the  myelinated  sciatic  nerve  of  the  frog  it  varies 


104  INTRODUCTION  TO  NEUROLOGY 

from  24  to  38  meters  per  second;  and  in  human  myelinated 
nerves  it  may  be  as  rapid  as  125  meters  per  second.  This  rate 
of  conduction  of  the  nervous  impulse  in  peripheral  nerves 
varies  greatly  with  different  animals,  with  different  nerves  in 
the  same  animal,  and  in  the  same  nerve  under  different  physio- 
logical conditions. 

The  reaction  time  required  for  the  performance  of  various  reflex  acts 
can  be  very  accurately  measured,  and  it  is  found  that  the  time  of  even  the 
simplest  reflex  is  considerably  greater  than  is  required  for  the  transmis- 
sion of  the  nervous  impulse  through  the  conductors  involved.  The  aver- 
age rate  of  conduction  in  human  nerves  is  probably  about  120  meters  per 
second,  and  the  simplest  reaction  times  which  have  been  measured  in 
psychological  laboratories  vary  between  0.1  and  0.2  second  (from  0.117 
to  0.188  for  reactions  to  touch,  and  from  0.120  to  0.182  for  reactions  to 
sound).  The  total  time  required  for  transmission  of  the  nervous  impulse 
through  the  nerve-fibers  involved  in  these  reactions  need  not  exceed  0.02 
second,  whence  it  appears  that  the  greater  part  of  the  reaction  time  is 
otherwise  consumed.  A  part  of  this  excess  time  is  required  to  overcome 
the  inertia  of  the  end-organs  (receptor  and  effectorj,  and  the  remainder 
is  used  in  the  central  nervous  system.  This  "central  pause"  is  charac- 
teristic of  all  reflexes  and,  in  fact,  has  a  profound  significance  in  connec- 
tion with  the  evolution  of  the  higher  associational  functions  of  the  brain. 
The  introduction  of  further  complexity  in  the  reaction,  of  whatever  sort, 
usually  lengthens  the  time  of  the  central  pause,  though  long  training  in 
making  a  discriminative  reaction  may  reduce  this  pause  almost  to  the 
time  of  a  simple  reaction. 

Many  attempts  have  been  made  to  determine  the  central  time  of  reac- 
tions of  different  degrees  of  complexity  by  subtracting  from  the  total 
time  in  each  case  the  probable  time  required  for  the  peripheral  processes 
and  by  subtracting  the  total  time  required  for  the  simpler  reactions  from 
the  total  time  taken  in  more  complex  discriminative  reactions.  But 
further  analysis  (particularly  more  critical  introspection)  has  shown  that 
in  these  human  reactions  the  problem  is  too  complex  to  be  resolved  by 
this  method  (see  Ladd  and  Woodworth,  1911,  p.  497). 

The  simpler  reflexes  of  lower  vertebrates  can  be  studied  physiologically, 
and  these  give  data  which  are  much  more  readily  analyzed  than  the  more 
complex  human  reactions.  In  the  case  of  the  simplest  reflex  obtainable 
in  the  spinal  cord  of  the  frog,  the  central  pause  was  estimated  by  Wundt 
to  be  onlj^  0.008  second,  i.  e.,  all  of  the  time  required  for  the  reaction  ex- 
cept this  interval  was  used  in  the  peripheral  apparatus.  But  in  a 
crossed  reflex,  where  the  reaction  occurs  on  the  opposite  side  of  the  bodj^ 
from  the  stimulus,  the  increased  complexity  of  the  central  process  con- 
sumed 0.004  second  additional. 

Miss  Buchanan  (1908),  with  more  accurate  methods  of  study,  finds  in 
the  frog  that  the  central  time  varies  between  .014  and  .021  second.  She 
also  measured  the  additional  latent  time  required  for  a  crossed  reflex, 
and  found  it  to  be  of  the  same  order  of  magnitude  as  the  latent  time  of  the 
simple  reflex  (instead  of  half  as  much  as  in  Wundt's  experiments),  that 
is,  the  crossed  reflex  required  about  twice  the  latent  time  in  the  spinal 
cord  as  the  uncrossed  reflex.     It  is  assumed  that  this  central  pause  in  the 


THE  GENERAL  PHYSIOLOGY  OF  THE  NERVOUS  SYSTEM    105 

uncrossed  reflex  is  consumed  chiefly  in  the  synapses  between  the  periph- 
eral sensory  and  the  peripheral  motor  neurons,  and  that  only  one  such 
synapse  is  involved  in  each  simple  reflex  connection  (a  two-neuron  cir- 
cuit, see  Fig.  1,  p.  26);  but  in  the  crossed  reflex  two  such  synapses  are 
involved  (a  three-neuron  circuit  such  as  the  pathway  from  d.r.2  to  v.r.V 
through  correlation  neuron  1  in  Fig.  61,  p.  14.5),  and  the  introduction 
of  the  second  synapse  doubles  the  time.  It  is,  therefore,  assumed  that 
it  requires  in  the  frog  between  .01  and  .02  second  for  the  nerv^ous  im- 
pulse to  pass  the  synapse  between  two  neurons  in  a  reflex  circuit. 

Turning  now  to  the  activities  of  the  nerve-cell  body,  it  will 
be  recalled  (p.  47)  that  here  the  chromophilic  substance  is  gen- 
erall}^  distributed  throughout  the  cytoplasm.  This  substance 
is  very  similar  to  that  of  the  chromatin  of  the  nucleus,  from 
which  it  is  said  to  be  derived  during  the  development  and 
functional  activity  of  the  neuron.  During  the  resting  state 
of  the  cell  it  and  other  reserve  materials  accumulate  in  the 
cytoplasm;  and  now,  when  the  cell  is  stimulated  to  activity, 
the  energy  thus  stored  up  may  be  Liberated  almost  instantly 
because  the  chemical  substances  necessarj'  for  the  reaction  are 
mdely  diffused  throughout  the  entire  mass  of  the  c}4oplasm. 

The  function  of  neurons,  as  compared  with  that  of  most 
other  cells  of  the  body,  may,  therefore,  be  described  as  of  the 
explosive  type.  A  word  of  explanation  will  render  the  analogy 
clear.  In  ordinaiy  combustion,  oxygen  is  supplied  to  the  sur- 
face of  the  burning  material,  say  a  blazing  log,  and  the  chemical 
process  of  burning  goes  on  only  as  fast  as  the  superficial  parts 
can  be  oxidized  and  removed.  But  explosive  substances  are 
chemically  so  constituted  that  as  soon  as  combustion  begins 
oxygen  is  liberated  in  the  interior  of  the  material  and  the  proc- 
ess of  oxidation  takes  place  almost  instantaneously  through- 
out the  entire  mass.  Similarly  in  the  nerve-cell,  the  processes 
of  metabolism  are  not  dependent  upon  the  slow  interchange  of 
substances  through  the  nuclear  membrane  between  the  cj'to- 
plasm  and  the  nuclear  plasm;  but  the  chromophilic  substance 
distributed  through  the  cytoplasm  permits  of  much  more  rapid 
responses.  The  organization  of  the  protoplasm  of  the  nerve- 
cell  is  such  that  a  very  small  stimulus  may  hberate  a  large 
amount  of  energy  with  explosive  suddenness.  The  energy  thus 
liberated  does  not  all  leave  the  cell,  but  part  of  it  is  directed 
into  the  axon,  which  is  thereby  excited  to  conduct  a  nervous 


106 


INTRODUCTION    TO    NEUROLOGY 


impulse  to  the  appropriate  end-organ  or  to  the  next  synapse, 
and  thence  to  a  second  neuron. 

The  conduction  of  nervous  impulses  within  the  central  nerv- 
ous system  in  some  cases  takes  place  through  well-defined  and 
insulated  bundles  of  fibers,  which  are  termed  tracts;  but  in  most 
cases  there  is  more  or  less  complexity  introduced  by  collateral 
avenues  of  discharge  to  other  specific  centers,  as  in  the  complex 
forms  of  reflex  systems  described  in  Chapter  IV,  or  by  a  more 
diffuse  type  of  irradiation  (p.  69).  The  organization  of  the 
central  nervous  system  is  such  that  in  general  the  excitation  of 
any  peripheral  sensory  neuron  may  be  transmitted  to  very  di- 


Fig.  39. — Diagram  of  an  arrangement  of  neurons  adapted  for  the  dis- 
tribution of  a  single  afferent  nervous  impulse  to  several  different  motor 
organs. 


verse  and  remote  parts  of  the  brain,  each  of  which  may  call 
forth  its  own  characteristic  form  of  response. 

The  physiological  effects  of  such  a  dispersal  of  an  incoming  nervous  im- 
pulse within  the  central  nervous  system  may  be  very  different,  depenumg 
on  the  connections  of  the  pathways  which  are  taken  by  the  neurons  ot  tne 
second  order.  If  these  pathways  diverge  so  that  the  stimulus  is  distrib- 
uted among  several  different  effector  systems,  this  would  tend  to  dis- 
perse the  energy  of  the  afferent  impulse  and  a  relatively  strong  stimulus 
is  necessary  to  call  forth  a  response.  This  is  the  situation  in  case  a  pain- 
ful prick  on  the  skin  of  the  face  calls  forth  reflex  movements  of,  say  (1) 
twitching  of  the  facial  muscles;'  (2)  turning  the  head  away,  and  (3)  a 


THE    GEN-ERAL   PHYSIOLOGY    OF   THE    NERVOUS    SYSTEM       107 

movement  of  the  hand  to  remove  the  irritant.  Here  the  stimulus  aris- 
ing at  a  single  point  in  the  skin  (Fig.  39)  is  distributed  to  three  widely 
separated  motor  centers  (M.l,  M.2,  M .3).  On  the  other  hand,  in  case 
the  stiumlus  received  Ijy  the  neuron  of  the  first  order  is  distributed  to 
several  neurons,  all  of  which  discharge  into  the  same  motor  center,  the 
stimulus  may  be  reinforced  because  each  neuron  of  the  second  order  may 
discharge  its  own  reserve  energy  in  such  a  way  as  to  send  out  a  stronger 
impulse  than  the  one  received,  so  that  the  total  discharge  into  the  motor 
center  is  greatly  strengthened  (Fig.  40).  Such  an  impulse  may  be  said 
to  accumulate  momentum  as  it  advances  like  an  avalanche  on  a  mountain 
slope,  and  hence  this  type  of  reaction  has  been  termed  by  Ram6n  y 
Cajal  "avalanche  conduction. "_  In  some  parts  of  the  brain  there  are 
verj'  special  mechanisms  for  this  sort  of  cumulative  discharge,  as  in  the 
cortex  of  the  cereliellum  (p.  214)  and  the  olfactory  bulb  (p.  242). 

The  intensity  of  nervous  discharge  in  all  of  its  forms  is  very  dependent 
upon  the  general  physiological  state  of  the  body,  some  conditions,  such 


5Kin 


muscle 


Fig.  40. — Diagram  of  the  mechanism  of  reinforcement  whereby  a  single 
weak  afferent  nervous  impulse  may  be  received  by  several  neurons  of  the 
second  order  which  discharge  their  greatly  strengthened  nervous  impulses 
into  a  single  final  common  path. 

as  fatigue  and  various  intoxications,  tending  to  depress  the  activity,  and 
other  conditions  tending  to  facilitate  it.  The  maintenance  of  good 
nervous  tone  is,  therefore,  essential  to  the  highest  efficiency.  Some  of 
these  physiological  agents  may  also  act  locally  on  particular  parts  of 
the  nervous  sj'stem  and  thus  determine  the  selection  of  one  instead  of 
another  out  of  several  possible  modes  of  response  in  the  variable  type  of 
behavior. 


Fatigue  of  nerve-cells  may  be  brought  about  in  two  ways, 
which  have  been  clearly  distinguished  by  Verworn:  (1)  by 
the  consumption  of  reserve  material  from  which  the  energy  of 
the  cell  is  derived  more  rapidly  than  this  material  can  be  re- 
stored, and  (2)  by  the  accumulation  of  waste-products  more 
rapidly  than  they  can  be  eliminated  from  the  cell.     These 


108  INTRODUCTION  TO  NEUROLOGY 

forms  of  fatigue  have  recently  been  named  by  Dolley  respec- 
tively "fatigue  of  excitation"  and  "fatigue  of  depression." 

In  his  interesting  discussion  of  neuro-muscular  fatigue,  Stiles 
(1914,  p.  101)  enumerates  several  particular  ways  (in  addition 
to  the  two  general  methods  just  mentioned)  by  which  fatigue 
may  be  brought  about,  among  which  are  the  following:  (1) 
fatigue  of  muscle-fibers,  (2)  fatigue  of  the  junction  of  the  motor 
nerve  with  the  muscle-fiber  at  the  motor  end-plate  (see  Fig. 
5,  p.  41),  (3)  fatigue  of  the  nerve-fibers,  (4)  fatigue  of  the  motor 
nerve-cells,  (5)  fatigue  of  the  synapses  between  the  nerve-cells, 
(6)  fatigue  of  the  sense  organs  and  afferent  apparatus,  (7)  fa- 
tigue of  the  centers  of  voluntary  control.  The  first,  second, 
fourth,  and  fifth  types  commonly  play  a  part  in  ordinary  fa- 
tigue, the  third  is  insignificant,  and  the  sixth  and  seventh  may 
be  present.  The  synapses  and  the  motor  end-plates  are  prob- 
ably especially  susceptible  to  fatigue  of  depression  by  toxic 
substances,  and  the  muscle-fibers  and  nerve-cell  bodies  to 
fatigue  of  excitation  by  consumption  of  their  material. 

A  resting  neuron  when  excited  to  activity  at  first  increases  in 
size  by  reason  of  the  stimulus  given  to  general  metabolic  activ- 
ity. The  first  signs  of  fatigue  result  from  the  exhaustion  of  the 
oxygen  supply  of  the  cells ;  then  follows  the  consumption  of  the 
reserve  food  materials,  chiefly  those  represented  in  the  chromo- 
philic  substance,  with  consequent  shrinkage  of  the  Nissl  bodies, 
as  these  are  seen  in  stained  preparations.  In  extreme  fatigue 
the  ultimate  dissolution  and  death  of  the  cell  may  be  hastened 
by  the  accumulation  of  toxic  products  of  cell  metabolism. 

It  appears  to  be  well  established  by  numerous  experimental  studies  that 
at  the  beginning  of  functional  activity  both  the  nucleus  and  the  cyto- 
plasm of  the  resting  neuron  are  enlarged,  and  that  with  the  onset  of 
fatigue  there  is  a  shrinkage,  especially  of  the  nucleus,  with  vacuolation  of 
the  cytoplasm  and  solution  of  the  Nissl  bodies  due  to  the  consumption 
of  the  chromophilic  substance  during  activity.  The  neurofibrils  are 
also  said  to  be  modified  during  functional  activity.  After  excessive 
activity  they  become  more  slender  and  apparently  increase  in  number, 
while  during  rest  and  after  hibernation  of  those  animals  which  have  this 
habit  the  neurofibrils  become  thicker  and  less  numerous. 

Cells  whose  chromophilic  substance  has  been  consumed  by  active 
function  may  after  rest  return  to  the  normal  form;  but  if  the  excitation  be 
carried  beyond  the  stage  of  normal  fatigue,  recovery  of  the  neuron  is  im- 
possible and  it  gradually  disintegrates,  resulting  in  the  permanent  en- 
feeblement  of  the  nervous  svstem. 


THE  GENERAL  PHYSIOLOGY  OF  THE  NERVOUS  SYSTEM   109 

The  observations  of  DoUey  have  suggested  to  him  that  the  volume  of 
the  nucleus  bears  a  constant  relation  to  the  volume  of  the  cytoplasm  in 
all  resting  nerve-cells  of  the  same  type.  In  varying  functional  states  of 
excitation  and  depression  this  mass  relation  is  disturbed  in  accordance 
with  the  formula:  Activity  finally  results  in  a  disturbance  of  the  normal 
nucleus-cytoplasmic  relation  in  favor  of  the  cytoplasm  (fatigue  of  exci- 
tation), while  depression  resulting  from  accumulated  toxins  finally  results 
in  a  disturbance  of  this  relation  in  favor  of  the  nucleus.  In  short,  the  de- 
pression of  the  neuron  by  any  form  of  intoxication  or  otherwise  gives  the 
converse  picture  of  structural  changes  from  that  presented  by  fatigue 
of  excitation. 

Most  of  the  physiological  work  which  has  been  done  upon  fatigue  has 
been  directed  toward  the  isolation  of  special  toxic  substances  such  as  in 
Dolley's  scheme  would  produce  "fatigue  of  depression."  It  has  been 
shown  that  prolonged  muscular  exertion  produces  toxins  (carbon  dioxid, 
lactic  acid,  and  others)  which  are  dissolved  in  the  blood  and  exert  a 
profound  depressing  influence  upon  all  of  the  tissues  of  the  body.  If  the 
blood  of  a  fatigued  animal  be  injected  into  or  transfused  with  a  perfectly 
fresh  animal  of  the  same  species,  the  latter  immediately  manifests  all 
the  signs  of  fatigue. 

It  is  often  taught  that  a  change  of  work  is  physiologically  equivalent  to 
complete  rest.  It  is  true  that,  so  long  as  one  is  well  within  the  limits  of 
extreme  fatigue,  a  change  of  work  will  prolong  efficiency  far  beyond  that 
which  would  be  possible  in  continuous  activity  of  a  single  nervous  or 
muscular  mechanism.  Some  experiments  show  that  mental  efficiency 
is  greatly  impaired  in  extreme  muscular  fatigue,  and,  conversely,  mus- 
cular power  is  greatly  weakened  after  long  sustained  mental  work. 
But  the  results  of  various  experiments  to  test  these  points  are  conflicting 
and  ambiguous,  and  the  problem  is  one  of  great  complexity.  Glandular 
secretions  are  also  apparently  often  reduced  in  extreme  fatigue,  thus,  for 
instance,  reducing  the  efficiency  of  the  digestive  organs.  These  effects 
are  doubtless  due  to  the  accumulation  of  toxic  products  in  the  blood,  pro- 
ducing a  true  "fatigue  of  depression"  throughout  the  entire  body. 

It  has  been  suggested  that  the  local  feelings  of  muscular  fatigue  are  due 
to  excitations  of  the  organs  of  the  muscular  sense  in  the  muscle  spindles  (p. 
92) ;  but  the  evidence  for  this  does  not  seem  very  convincing. 

The  experiments  of  Dolley  suggest  to  him,  further,  that  the  more  highly 
differentiated  nerve-centers  are  more  susceptible  to  the  structural  altera- 
tions of  fatigue  than  are  those  of  the  lower  reflex  systems.  It  is  a  well- 
known  fact  that  sustained  mental  work  produces  the  subjective  evi- 
dences of  fatigue  more  promptlj^  than  does  muscular  work,  and  that 
during  severe  mental  training  one  is  more  apt  to  go  "stale"  than  during 
physical  training.  This  principle  has  been  widel.y  recognized  in  the 
provision  of  short  working  hours  and  frequent  holidays  for  pupils  and 
teachers  in  our  schools;  it  should  be  still  further  extended,  especially  in  com- 
mercial and  professional  life.  Its  neglect  is  in  large  measure  responsible 
for  the  prevalence  of  various  forms  of  nervous  breakdown. 

The  early  fatigue  of  the  higher  voluntary  centers  is  particularly  evident 
in  young  children,  where  continuous  sustained  attention  is  impossible 
except  for  very  short  periods.  By  training,  these  periods  can  be  greatly 
lengthened,  the  nervous  mechanism  involved  here  probably  being  the 
acquisition  of  a  wider  range  of  associations  related  with  tlie  subject  which 
occupies  the  focus  of  attention,  so  that  individual  neurons  or  s>'stems  of 


110  INTRODUCTION  TO  NEUROLOGY 

neurons  which  participate  in  the  functional  complex  may  be  temporarily 
rested  while  other  related  systems  are  broxight  into  maximum  activity, 
without  thereby  interrupting  the  continuous  progress  of  the  train  of 
thought. 

The  neurological  basis  of  sleep  is  at  present  wholly  unknown, 
though  the  physiological  phenomena  seem  to  be  in  many  re- 
spects analogous  with  those  of  fatigue.  Of  the  various  theories 
which  have  been  suggested,  the  two  which  have  excited  great- 
est interest  are:  (1)  the  belief  that  some  soluble  toxin  is  pro- 
duced during  waking  hours  which  induces  sleep  by  a  process 
similar  to  that  of  the  ''fatigue  of  depression,"  and  (2)  the  doc- 
trine of  the  retraction  of  the  neuron,  which  teaches  that  during 
sleep  (and  according  to  some  authors  in  less  measure  during 
fatigue  also)  the  dendrites  of  the  neurons  retract  toward  their 
cell  bodies  and  away  from  contact  with  the  axons  of  other 
neurons  with  which  they  are  in  synaptic  union,  thus  increasing 
the  resistance  to  nerve  conduction  at  the  synapse. 

Many  physiological  experiments  show  that,  though  the  pre- 
disposition to  sleep  may  be  brought  about  by  the  accumulation 
of  toxins  in  the  blood  or  by  other  general  causes,  the  actual  fall- 
ing asleep  is  due  to  some  other  factor.  Fatigue  of  the  vaso- 
motor center  has  been  suggested  as  the  real  physiological  cause 
of  sleep.  No  adequate  proof  of  any  of  these  theories  has  been 
brought  forward. 

The  view  formerly  prevalent  that  sleep  is  due  to  cerebral 
anemia  seems  to  have  been  disproved  by  the  careful  experi- 
ments of  Shepard  on  the  volume  of  the  brain  during  waking 
and  sleeping  conditions.  The  blood  supply  sent  to  the  brain 
was  measured  by  studying  the  volume  of  the  brain  in  two  men 
whose  skulls  had  been  trephined.  In  these  cases  there  was  a 
marked  increase  of  the  volume  of  the  brain  during  sleep,  the 
increase  being  at  its  maximum  from  15  to  25  minutes  after  the 
subject  fell  asleep,  and  thereafter  diminishing  somewhat, 
though  always  remaining  greater  during  sleep  than  when 
awake. 

The  numerous  theories  regarding  the  neurological  processes 
taking  place  in  the  cerebral  cortex  during  the  progress  of  such 
mental  functions  as  attention,  association  of  ideas,  etc.,  are 
likewise  as  yet  entirely  unproved.     It  has  been  suggested  that 


THE  GENERAL  PHYSIOLOGY  OF  THE  NERVOUS  SYSTEM   111 

during  cerebral  function  the  resistance  of  souk;  pathways  may- 
be diminished  by  the  ameboid  outgrowths  of  the  dendrites 
so  as  to  effect  more  intimate  synaptic  union  with  the  physio- 
logically related  neurons,  while  the  resistance  of  other  paths 
may  be  increased  by  the  retraction  of  dendrites  from  their 
synapses.  Others  believe  that  the  neuroglia  may  participate 
in  the  process  by  thrusting  out  ameboid  processes  between  the 
nervous  terminals  in  the  synapses  and  thus  increasing  the 
resistance.  Lugaro  has  suggested  a  different  interpretation,  in 
accordance  with  which  during  sleep  there  is  a  generally  diffused 
extension  of  all  nervous  processes,  thus  providing  for  tne  uni- 
form diffusion  of  incoming  stimuli,  while  in  the  state  of  atten- 
tion all  of  these  processes  retract  save  those  which  are  directed 
in  some  definite  direction,  thus  narrowing  the  stream  of  nerv- 
ous discharge  so  as  to  intensify  it  and  direct  it  into  the  appro- 
priate centers.  There  is  no  direct  evidence  for  any  of  these 
theories,  and  the  scientifically  correct,  attitude  toward  them  is 
frankly  to  admit  that  at  present  we  do  not  know  what  physio- 
logical processes  are  involved  in  any  of  these  functions. 

C hemotaxis.— The  development  and  evolution  of  the  brain  suggest 
many  physiological  questions  which  are  still  far  from  satisfactory  solution. 
It  has  often  been  asked,  for  instance,  how  the  nerve-fibers  which  arise  from 
cell  bodies  in  one  part  of  the  nervous  system  find  their  way  through 
long  and  often  devious  courses  to  remote  parts  and  there  effect  phj^sio- 
logical  relations  with  the  appropriate  centers  necessary  for  establishing 
useful  reflexes.  Similarly  the  peripheral  nerves  are  known  to  grow  out- 
ward toward  their  respective  areas  of  distribution  and  one  wonders  how 
they  find  their  way  and  arc  able  to  reach  the  proper  end-organ.  Num- 
erous observations  and  experiments  show  that  this  is  not  a  matter  of 
chance,  but  that  the  nerves  appear  to  seek  out  their  appropriate  end- 
organs. 

This  problem  is  very  complex  and  doubtless  many  factors  operate. 
Among  these  is  probably  the  familiar  biological  principle  of  chemotaxis. 
Many  organisms  or  parts  of  organisms  grow  toward  certain  specific 
kinds  of  chemical  emanations;  thus,  plant  roots  in  the  soil  will  grow 
toward  water.  This  movement  is  called  chemotaxis  and  it  has  been  as- 
sumed that  a  similar  manifestation  of  biochemical  affinity  is  operative  in 
the  developing  nervous  svstem  (see  Ram6n  y  Cajal,  S5'^steme  Nerveux, 
vol.  i,  p.  657). 

Many  organs  of  the  adult  body  are  known  to  secrete  specific  soluble 
chemical  substances  termed  hormones,  which  diffuse  throughout  the 
lymph  or  blood  and  call  forth  functional  activity  in  remote  organs  (see 
p.  249).  It  is  possible  that  during  development  of  the  body  the  organs, 
as  soon  as  definite  stages  of  growth  are  reached,  secrete  similar  substances 
which  diffuse  through  the  surrounding  tissue  and  each  of  which  has  a 
chemotactic  affinity  for  a  certain  type  of  developing  neurons.     Thus, 


112  INTRODUCTION  TO  NEUROLOGY 

the  developing  muscles  may  secrete  a  substance  to  which  the  motor  neu- 
rons of  the  spinal  cord  react  by  a  growth  of  their  embrj^onic  axones  to- 
ward the  source  of  the  stimulating  material. 

Neurobiotaxis. — In  the  course  of  the  evolution  of  the  vertebrate  nerv- 
ous system  numerous  groups  of  cell  bodies  ("nuclei")  with  specific 
functions  have  moved  from  their  primitive  positions  to  new  locations. 
This  is  quite  a  different  thing  from  the  chemotactic  outgrowth  of  nerve 
fibers  described  above.  Many  of  these  phylogenetic  migrations  of 
nerve-cell  bodies  have  been  accurately  described  by  Kappers  and  his 
school  and  are  ascribed  to  a  factor  termed  neurobiotaxis.  This  principle 
is  that  in  the  course  of  phylogeny  cell  bodies  tend  to  migrate  in  the  di- 
rection from  which  they  habitually  receive  their  stimuli;  i.  e.,  in  the  di- 
rection taken  by  their  dendrites.  If  there  is  a  change  in  the  direction 
from  which  a  given  nucleus  receives  its  chief  stimuli,  the  nucleus  as  a 
whole  will  tend  to  move  toward  the  new  source  of  excitation  and  away 
from  the  old.  Many  illustrations  are  given  in  the  papers  by  Kappers 
(1914)  and  Black  (1917)  and  the  works  there  cited. 

This  shortening  of  the  dendrites  is  doubtless  due  in  part  to  the  fact 
that  these  processes  of  the  neuron  are  structurally  less  perfectly  adapted 
to  transmit  nervous  impulses  than  are  the  axons  (see  p.  41).  In  this  con- 
nection it  is  interesting  to  recall  that  the  neurons  of  the  spinal  and  cranial 
ganglia,  which  do  not  exhibit  neurobiotactic  migrations,  have  long 
dendrites  whose  structure  is  similar  to  that  of  their  axons  and  are  pre- 
sumabl}!-  equallj^  good  conductors.  But  other  factors  also  appear  to 
be  present  which  are  critically  reviewed  by  Kappers  in  his  latest  contri- 
bution (1917)  and  these  factors  seem  to  him  to  be  related  with  the  elec- 
trical phenomena  of  nervous  conduction  (galvanotaxis). 

Summary. — The  forms  assumed  by  neurons  are  shaped  in 
part  by  their  nutritive  requirements  and  in  part  by  their  func- 
tional connections.  The  metaboHsm  of  nervous  protoplasm, 
as  measured  by  its  CO2  output,  is  found  to  be  as  active  in  nerve- 
fibers  as  in  the  cell  bodies.  Tn  a  nerve-fiber  the  metabolic 
activity  is  found  to  be  greatly  increased  during  the  transmis- 
sion of  a  nervous  impulse;  and  nervous  conduction  evidently 
involves  a  chemical  change  in  the  conducting  fiber.  The  rate 
of  transmission  of  a  nervous  impulse  depends  on  the  structure 
and  physiological  state  of  the  nerve-fiber  involved.  The 
metabohc  activity  of  the  nerve-cells  is  of  a  very  different  sort 
from  that  of  nerve-fibers,  and  may  be  characterized  as  of  the 
explosive  type.  There  are  at  least  two  factors  involved  in  the 
fatigue  of  the  nervous  system:  (1)  fatigue  of  excitation,  re- 
sulting from  the  consumption  of  the  materials  of  its  proto- 
plasm, and  (2)  fatigue  of  depression,  resulting  from  the  accu- 
mulation of  toxic  products  of  cellular  activity.  Each  of  these 
processes  produces  its  own  very  special  series  of  morphological 


THE  GENERAL  PHYSIOLOGY  OF  THE  NERVOUS  SYSTEM   113 

changes  in  the  neurons.     The  neurological  functions  involved 
in  sleep  and  the  higher  mental  processes  are  as  yet  unknown. 

Literature 

Black,  D.  1917.  The  Motor  Nuclei  of  the  Cerebral  Nerves  in  Phy- 
logeny.  A  Study  of  the  Phenomena  of  Neurobiotaxis.  I.  Cyclostomi 
and  Pisces,  Jour.  Comp.  Neur.,  vol.  xxvii,  pp.  467-564.  II.  Amphibia, 
Ibid.,  vol.  xxviii,  pp.  379-427. 

Buchanan,  Florence.  1908.  On  the  Time  Taken  in  Transmission 
of  Reflex  Impulses  in  the  Spinal  Cord  of  the  Frog,  Quart.  Jour.  Exp. 
Physiol.,  vol.  i,  pp.  1-66. 

Child,  C.  M.  1914.  Susceptibihty  Gradients  in  Animals,  Science, 
N.  S.,  vol.  xxxix,  No.  993,  pp.  73-76. 

Dockeray,  F.  C.  1915.  The  Effects  of  Physical  Fatigue  on  Mental 
Efficiency,  Kansas  Univ.  Science  Bui.,  vol.  ix,  No.  17,  pp.  197-243. 

Dolley,  D.  H.  1911.  Studies  on  the  Recuperation  of  Nerve-cells 
After  Functional  Activity  from  Youth  to  Senility,  Jour.  Med.  Research, 
vol.  xxiv,  pp.  309-343. 

• — .  1914.  On  a  Law  of  Species  Identity  of  the  Nucleus-plasma  Norm 
for  Nerve-cell  Bodies  of  Corresponding  Types,  Jour.  Comp.  Neur., 
vol.  xxiv,  pp.  445-501. 

— .  1914.  Fatigue  of  Excitation  and  Fatigue  of  Depression,  Intern. 
Monatsschrift  f.  Anat.  u.  Physiol.,  Bd.  31,  pp.  35-62. 

Donaldson,  H.  H.  1899.  The  Growth  of  the  Brain,  New  York, 
chapters  xiv  to  xvii. 

Hodge,  C.  F.  1892.  A  Microscopical  Study  of  Changes  Due  to 
Functional  Activity  in  Nerve-cells,  Jour.  Morphology,  vol.  vii,  pp. 
95-168. 

Kappers,  C.  U.  a.  1914.  Phenomena  of  Neurobiotaxis  in  the  Cen- 
tral Nervous  System,  Proc.  XVII.  Intern.  Congress  of  Medicine,  Sec- 
tion I.     Anat.  and  Embryology,  pp.  109-122,  London. 

— .  1917.  Further  Contributions  on  Neurobiotaxis.  IX.  An  At- 
tempt to  Compare  the  Phenomena  of  Neurobiotaxis  with  other  Phe- 
nomena of  Taxis  and  Tropism.  The  Dynamic  Polarization  of  the  Neu- 
ron, Jour.'Comp.  Neur.,  vol.  xxvii,  pp.  261-298. 

Ladd,  G.  T.,  and  Woodworth,  R.  S.  1911.  Elements  of  Physio- 
logical Psychology,   New  York. 

Shepard,  John,  F.  1914.  The  Circulation  and  Sleep,  New  York, 
The  Macmillan  Co. 

Stiles,  P.  G.  1914.  The  Nervous  Sj'stem  and  Its  Conservation, 
Philadelphia. 

Tashiro,  S.  1913.  Carbon  Dioxide  Production  from  Nerve-fibers 
when  Resting  and  when  Stimulated;  a  Contribution  to  the  Chemical 
Basis  of  Irritabilitv,   Amer.  Jour,  of  Physiol.,  vol.  xxxii,  pp.  107-136. 

— ,     1917.     A  Chemical  Sign  of  Life,  University  of  Chicago  Press. 

Tashiro,  S.,  and  Ad.\ms,  H.  S.  1914.  Carbon  Dioxide  Production 
from  the  Nerve-fiber  in  a  Hydrogen  Atmosphere,  Amer.  Jour,  of  Physiol., 
vol.  xxxiv,  pp.  405-413. 

.     1914.     Comparison  of  the  Carbon  Dioxide  Output  of  Nerve- 
fibers  and  Ganglia  in  Limulus,  Jour,  of  Biological  Chemistry,  vol.  xviii, 
pp.  329-334. 
8 


CHAPTER  VII 

THE  GENERAL  ANATOMY  AND  SUBDIVISION  OF  THE 
NERVOUS  SYSTEM 

On  merely  topographic  grounds  the  nervous  organs  are  di- 
vided into  the  central  iiervous  system,  or  axial  nervous  system, 
comprising  the  brain  and  spinal  cord,  and  the  'peripheral  nerv- 
ous system,  including  the  cranial  and  spinal  nerves,  their  gan- 
gUa  and  peripheral  end-organs,  and  the  sympathetic  nervous 
systein.  The  nerves  are  simply  conductors,  putting  the  end- 
organs  into  physiological  connection  with  their  respective 
centers.  The  general  form  of  the  human  central  nervous  sys- 
tem and  its  connections  with  the  peripheral  nerves  are  seen  in 
Fig.  41.  The  nerves  connected  with  the  spinal  cord  are  the 
spinal  nerves,  those  connected  with  the  brain  are  the  cranial  or 
cerebral  nerves,  and  both  of  these  systems  of  nerves  together 
are  called  the  cerebrospinal  nerves,  in  contrast  with  the  sym- 
pathetic nerves,  which  latter  may  or  may  not  be  connected 
with  the  central  nervous  system  (see  p.  249). 

The  central  nervous  system  is  the  great  organ  of  correlation 
and  integration  of  bodily  processes.  Its  primitive  form  in  ver- 
tebrates is  a  simple  tube,  and  this  is  the  form  shown  in  an  early 
human  embryo  (see  Fig.  46,  p.  125).  The  original  tubular 
form  is  but  little  modified  in  the  trunk  region  of  all  vertebrates, 
where  the  spinal  cord  (medulla  spinalis)  is  formed  by  a  toler- 
ably uniform  thickening  of  the  lateral  walls  of  the  tube  (see 
Figs.  41,  58).  But  in  the  head  region  the  brain  (encephalon)  is 
formed  by  the  very  unequal  thickening  of  different  parts  of  the 
walls  of  the  tube  and  by  various  foldings  brought  about  there- 
by. The  general  arrangement  of  the  human  central  nervous 
system  at  successive  stages  of  development  is  seen  in  Figs. 
47-51. 

The  external  form  of  the  brain  has  been  shaped  by  the  space 
requirements  of  the  nerve-cells  and  fibers  which  make  up  its 

114 


SUPERIOR  CERVICAL  SYM- 
PA  THETIC  GANGLION 


MIDDLE   CERVICAL  SYMPATHETIC 
GANGLION 


INFERIOR   CERVICAL  SYMPA- 
THETIC GANGLION 


f 
I 

OANGLIATED  CORD  ^ 
1 
I 


-/  -  I  CERVICAL  NERVB 


I  THORACIC  NERVE 


GANGLION  - 


I  LUMBAR  NERVB 


- -I  SACRAL  NERVE 


•n  COCCYGEAL  NERVE 
FILUM  TEEMINALE 

Fig.  41. — The  human  central  nervous  system  from  the  ventral  side, 
illustrating  also  its  connections  with  the  cerebro-spinal  nerves  and  with 
the  .sympathetic  nervous  system,  the  latter  drawn  in  black.  (After  Allen 
Thompson  and  Rauber,  from  Morris'  Anatomy.) 


116  INTRODUCTION  TO  NEUROLOGY 

substance.  A  group  of  nerve-cells  which  performs  a  single 
function  is  often  spoken  of  as  the  "center"  of  that  function; 
but  it  should  be  borne  in  mind  that  this  does  not  imply  that 
this  function  resides  exclusively  in  that  place.  These  func- 
tions are  all  more  or  less  complex  and  the  "center"  is  usually 
the  region  where  various  nervous  impulses  are  received  and 
redistributed;  it  is,  therefore,  roughly  analogous  with  the 
switchboard  of  an  electric  plant. 

The  nerve-fibers  which  conduct  nervous  impulses  toward  a 
given  center  are  called  afferent,  and  those  which  conduct  away 
from  the  center  are  called  efferent  with  reference  to  that  center. 
Most  of  the  peripheral  nerves  are  mixed,  in  the  sense  that  they 
carry  both  afferent  and  efferent  fibers  with  reference  to  the 
central  nervous  system.  The  efferent  fibers  may  excite  move- 
ment in  muscles  (motor  fibers)  or  secretion  in  glands  (excito- 
glandular  fibers);  other  efferent  fibers  which  check  the  action 
of  the  organ  to  which  they  are  distributed  are  called  inhibitory 
fibers.  The  afferent  fibers  of  the  peripheral  nerves  are  often 
called  sensory  fibers,  though  it  must  be  borne  in  mind  that  their 
excitation  is  not  always  followed  by  sensations  or  other  con- 
scious   processes. 

The  vertebrate  nervous  system  when  examined  in  the  fresh 
condition  is  found  to  be  made  up  of  white  matter  (substantia 
alba)  and  gray  matter  (substantia  grisea),  the  white  matter 
containing  chiefly  nerve-fibers  with  myelin  sheaths  (see  p.  49) 
and  the  gray  matter  nerve-cell  bodies  and  unmyelinated 
fibers.  The  centers  are,  therefore,  generally  gray  in  color 
and  the  intervening  parts  of  the  central  nervous  system  are 
white. 

A  group  of  nerve-cells  constituting  a  center  as  above  described  is  often 
called  a  "nucleus,"  a  term  which  has  nothing  to  do  with  the  nuclei  of  the 
individual  cells  (see  p.  40)  of  which  the  center  is  composed.  Some  crit- 
ical writers  use  the  word  "nidulus"  (originally  suggested  by  C.  L. 
Herrick)  or  "nidus"  (Spitzka)  for  such  a  center,  thus  avoiding  the  am- 
biguity in  the  use  of  the  word  nucleus.  The  term  "ganglion"  is  also 
sometimes  used  for  nuclei  or  centers  within  the  brain  _  (ganglion  habe- 
nulse,  ganglion  interpedunculare,  etc.),  but  this  usage  is  objectionable, 
for  the  use  of  the  word  ganglion  in  vertebrate  neurology  should  be  re- 
stricted to  collections  of  neurons  outside  the  central  nervous  system,  such 
as  the  ganglia  of  the  cranial  and  spinal  nerves  and  the  sympathetic 
ganglia. 

A  nucleus  from  which  nerve-fibers  arise  for  conduction  to  some  remote 


ANATOMY    AND    SUBDIVISION    OF   NERVOUS    SYSTEM  1  1 7 

part  of  the  nervous  system  is  called  the  nucleus  of  origin  of  these  fibers; 
conversely,  a  nucleus  into  which  nervous  impulses  are  discharged  by 
fibers  arising  elsewhere  is  the  terminal  nucleus  of  those  fibers.  Any 
correlation  center  is,  therefore,  a  terminal  nucleus  for  its  afferent  fibers 
and  a  nucleus  of  origin  for  its  efferent  fibers. 

The  centers  or  nuclei  within  the  brain  are  of  two  general 
sorts:  (1)  primary  centers  and  (2)  centers  of  adjustment. 
The  second  class  includes  centers  of  correlation  and  coordina- 
tion (p.  36).  The  primary  centers  are  directly  connected 
with  peripheral  nerves,  either  as  terminal  nuclei  of  afferent 
fibers  or  as  nuclei  of  origin  of  efferent  fibers  (see  pp.  44,  116). 
The  elements  out  of  which  most  acts  are  compounded  are 
reflexes  (see  p.  59),  and  in  the  simplest  of  these  reflexes  a 
sensory  nervous  impulse  received  from  the  periphery  by  a 
terminal  nucleus  may  be  passed  on  to  a  nucleus  of  origin  and 
thence  directly  to  the  organ  of  response;  but  in  more  complex 
reflexes  the  incoming  nervous  impulse  is  first  transmitted  from 
the  terminal  nucleus  to  a  correlation  center,  where  it  may  meet 
other  types  of  sensory  impulses  and  then  be  discharged  into  any 
one  of  several  possible  motor  pathways.  For  illustrations  of 
these  types  of  connection  see  Chapter  IV. 

In  general,  ganglia  or  nerve-centers  are  interpolated  in  con- 
duction pathways  only  where  some  complication  of  the  reac- 
tion is  to  be  provided.  The  conduction  path  is  usually  here 
interrupted  by  synapses  and  various  forms  of  correlation  or 
coordination  mechanisms  are  present  (see  p.  36  and  Chapter 
IV).  Many  of  the  sympathetic  ganglia  provide  the  mechan- 
ism for  local  reflexes  in  which  the  central  nervous  system  does 
not  participate  (p.  250).  The  spinal  ganglia  (see  Fig.  1,  p.  26) 
are  often  regarded  as  merely  trophic  centers  for  the  maintenance 
of  the  fibers  of  the  peripheral  nerves ;  but  they  evidently  have 
functions  of  correlation  in  addition  to  this,  for  numerous  syn- 
apses between  sympathetic  and  cerebro-spinal  neurons  occur 
here  (see  p.  254  and  Fig.  109)  which  play  a  part  in  the  correla- 
tion of  visceral  and  somatic  reactions. 

The  primary  centers  and  the  simpler  adjusting  centers  of  the 
brain  can  be  studied  much  more  readily  in  the  brains  of  fishes, 
which  lack  the  cerebral  cortex  whose  enormous  development  in 
the  human  brain  has  obscured  the  relations  and  connections  of 


118 


INTRODUCTION   TO    NEUROLOGY 


the  more  primitive  reflex  apparatus.     Figures  42,  43,  and  44 
illustrate  the  relations  of  the  principal  sense  organs  to  the 


lat.vce.^ 


Fig.  42. — Dissection  of  the  brain  and  cranial  nerves  of  the  dogfish, 
Scyllium  catulus.  The  right  eye  has  been  removed.  The  cut  surfaces 
of  the  cartilaginous  skull  and  spinal  column  are  dotted.  cZ.l-c/.5,  bran- 
chial (gill)  clefts;  ep.,  epiphysis;  ext.rect.,  external  rectus  muscle  of  the 
eyeball;  gl.ph.,  glossopharyngeal  nerve;  hor.can.,  horizontal  semicircular 
canal;  hy.mnd.VII,  hyomandibular  branch  of  the  facial  nerve;  inf. obi., 
inferior  oblique  muscle;  int.rect.,  internal  rectus  muscle;  lat.vag.,  lateral 
line  branch  of  the  vagus  nerve;  mnd.V,  mandibxilar  branch  of  the  trigeminal 
nerve;  mx.V,  maxillary  branch  of  trigeminus;  olf.cps.,  olfactory  capsule; 
olf.s.,  olfactory  sac;  oph.V.VII,  superficial  ophthalmic  branches  of  the 
trigeminal  and  facial  nerves;  path.,  trochlear  nerve  (patheticus) ;  pl.VII, 
palatine  branch  of  facial  nerve;  s.obl.,  superior  oblique  muscle;  sp.,  opening 
of  spiracle;  sp.co.,  spinal  cord;  spir.,  spiracle;  s.rect.,  superior  rectus  muscle; 
vag.,  vagus  nerve;  vest.,  vestibule.  (After  Marshall  and  Hurst,  from  Parker 
and  Haswell's  Zoology.) 

brain  in  a  small  shark,  the  common  marine  dogfish.  Figures 
42  and  43  (on  the  right  side)  illustrate  the  arrangement  of  the 
principal  roots  and  branches  of  the  cranial  nerves.     On  the  left 


ANATOMY   AND    SUBDIVISION    OF   NERVOUS   SYSTEM 


119 


r.  ophthal.  superfic.  V 
r.  ophthal.  superfic.  VII 

n.  terminalis 

r.  ophthal.  profundus  V 

Optic  nerve  (n.  II) 


r.  maxillaris  V 
r.  mandib.  V 


Supra-orbital  trunk 

Infra-orbital  trunk 
Ganglion  V 
r.  palatinus  VII 
Gang,  geniculi  VII 
Gang,  later.  VII 
r.  prespirac.  VII 


Spinal 
cord 


-Spiracle 

-r.  hyomandib.  VII 

n.  IX 
n.  X 
r.  lateralis  X 


r.  branchialis  X 


r.  intestinalis  X 


Fig.  43. — Diagram  of  the  brain  and  sensory  nerves  of  the  smooth  dog- 
fish, Mustelus  canis,  from  above.  Natural  size.  The  Roman  numerals 
refer  to  the  cranial  nerves.  The  olfactory  part  of  the  brain  is  dotted,  the 
visual  centers  are  shaded  with  oblique  cross-hatching,  the  acoustico-lateral 
centers  with  horizontal  lines,  the  visceral  sensory  area  with  vertical  lines, 
and  the  general  cutaneous  area  is  left  unshaded.  On  the  right  side  the 
lateral  line  nerves  arc  drawn  in  black,  the  other  nerves  are  unshaded. 


120 


INTRODUCTION    TO    NEUROLOGY 


side  of  Fig,  43  the  relations  of  the  nose,  the  eye,  and  the  ear  to 
the  brain  are  indicated;  and  Fig.  44  shows  an  enlarged  side  view 
of  the  brain  and  the  sensory  roots  of  the  cranial  nerves. 

In  fishes  there  is  a  system  of  small  sensory  canals  widely  dis- 
tributed under  the  skin.  These  contain  sense  organs  some- 
what similar  to  those  in  the  semicircular  canals  of  the  internal 
ear,  and  their  functions  are  probably  intermediate  between 
those  of  the  organs  of  touch  in  the  skin  and  those  of  the  internal 
ear,  responding  to  water  vibrations  of  slow  frequency  and 
probably  assisting  in  the  orientation  of  the  body  in  space. 
These  are  the  lateral  line  canals.  They  are  innervated  by 
special  roots  of  the  VII  and  X  pairs  of  cranial  nerves  (the 


Fig.  44. — The  same  brain  as  Fig.  43  seen  from  the  side  and  sHghtly  enlarged. 

lateralis  roots  of  these  nerves),  which  are  drawn  in  black  in 
Figs.  43  and  44.  The  other  nerves  are  lightly  shaded  or 
white.  The  lateral  line  organs  and  their  nerves  are  entirely 
absent  in  higher  vertebrates  (see  p.  222). 

For  a  fuller  account  of  the  nervous  system  of  the  dogfish, 
with  more  detailed  drawings  of  the  components  of  the  cranial 
nerves,  see  Herrick  and  Crosby  (1918,  pp.  16-36). 

The  lateral  line  nerves  and  the  acoustic  nerve  (VIII  pair)  in 
fishes  terminate  in  a  common  center  within  the  brain  (the 
acoustico-lateral  area),  which  is  shaded  with  horizontal  cross- 
hatching  in  Figs.  43  and  44.  The  nerves  of  general  cutaneous 
sensibility  also  terminate  in  a  particular  region  which  is  un- 
shaded and  marked  "general  cutaneous  area."     The  visceral 


ANATOMY    AND    SUBDIVISION    OF   NERVOUS   SYSTEM  121 

nerves  from  the  gills,  stomach,  etc.,  all  enter  a  single  "  visceral 
area,"  which  is  shaded  with  vertical  lines.  The  eye  is  also 
connected  with  a  special  region  in  the  midbrain,  the  "optic 
lobe,"  which  is  shaded  with  oblique  cross-hatching;  and  the 
nose  is  connected  with  a  part  of  the  forebrain  which  is  stippled. 

We  may,  therefore,  recognize  in  this  fish  a  ''nose  brain," 
an  "eye  brain,"  an  "ear  brain,"  a  "visceral  brain,"  and  a 
"skin  brain,"  each  of  these  peripheral  organs  having  enlarged 
primary  terminal  nuclei  which  make  up  definite  parts  of  the 
brain  substance.  Remembering  that  the  primitive  brain  was 
a  simple  tubular  structure,  we  observe  that  each  one  of  the 
chief  sense  organs  and  each  group  of  similar  sense  organs  sends 
sensory  nerves  inward  to  terminate  in  a  special  part  of  the 
wall  of  the  primitive  neural  tube,  and  that  here  a  thickening 
of  the  wall  of  the  tube  has  taken  place  to  provide  space  for  the 
appropriate  terminal  nucleus.  It  may  be  noticed,  further, 
that  all  of  these  structures  (except  a  part  of  the  olfactory 
centers)  lie  in  the  dorsal  part  of  the  brain.  An  examination  of 
the  primary  motor  centers  would  show  that  they  are  distrib- 
uted in  a  somewhat  similar  fashion  along  the  ventral  part  of 
the  brain. 

The  facts  just  recounted  give  a  clear  picture  of  the  pattern  of 
functional  localization  of  the  primary  reflex  centers  in  a  simple 
type  of  brain,  and  they  show  that  all  of  the  more  obvious  parts 
of  this  brain  except  the  cerebellum  are  in  simple  direct  relation 
with  particular  peripheral  organs.  In  other  words,  nearly  the 
whole  of  this  brain  is  directly  concerned  with  simple  reflexes 
and  (aside  from  the  cerebellum)  no  large  centers  for  the  higher 
types  of  adjustments  are  present.  The  primary  reflex  centers 
are  found  to  be  arranged  in  accordance  with  essentially  the 
same  pattern  in  the  human  and  all  other  higher  brains,  though 
in  these  cases  the  pattern  is  modified  and  much  obscured  bj^  the 
presence  of  greatly  enlarged  correlation  centers,  of  which  the 
cerebral  cortex  is  the  chief.  The  structure  and  significance 
of  the  cerebral  cortex  form  the  theme  of  the  last  three  chapters 
of  this  work. 

The  central  nervous  system  of  the  earliest  vertebrates  was 
probably  a  simple  longitudinal  tube  of  nervous  tissue  with 
which  the  i^eripheral  nerves  were  connected  in  a  segmental 


122  INTEODUCTION  TO  NEUROLOGY 

fashion  (see  p.  30).  This  is  the  permanent  form  of  the  spinal 
cord  and  its  nerves  in  all  vertebrates  (see  p.  136  and  Fig.  41). 
In  the  brain  the  enlargement  of  the  primary  reflex  centers  and 
of  the  correlation  centers  directly  related  to  them  has  changed 
the  form  of  the  tube  and  disturbed  the  primitive  segmental 
arrangement  of  the  cranial  nerves,  as  is  indicated  in  Figs.  43 
and  44.  Nevertheless,  this  more  ancient  part  of  the  brain  is 
sometimes  called  the  segmental  apparatus,  to  distinguish  it 
from  two  very  large  coordination  and  correlation  mechanisms 
which  are  of  later  evolutionary  origin,  namely,  the  cerebellar 
cortex  and  the  cerebral  cortex,  which  are  termed  supraseg- 
mental  structures  (A.  Meyer). 

The  segmental  apparatus  of  even  the  lowest  vertebrates  shows  the 
regional  differentiation  suggested  in  Figs.  43  and  44,  each  of  these  re- 
gions being  elaborated  in  correspondence  with  the  particular  type  of  end- 
apparatus  in  connection  with  it. 

In  addition  to  these  particular  centers  of  reflex  correlation,  there  are 
provided  higher  centers  for  the  integration  of  all  activities  of  the  body 
as  a  whole  (see  p.  37).  In  lower  vertebrates  this  integration  is  very 
simply  manifested,  each  part  of  the  central  nervous  system  possessing 
much  more  complete  autonomy  than  is  the  case  in  man  (cf.  Herrick 
and  Coghill  cited  on  pp.  71,  199).  As  we  pass  from  lower  to  higher 
vertebrates  the  chief  integrating  center  shifts  its  position  from  the  mid- 
brain in  fishes  to  the  thalamus  and  corpus  striatum  complex  in  reptiles 
and  birds,  and  finally  to  the  cerebral  cortex  in  mammals.  These  in- 
tegrating centers  increase  in  size  and  functional  importance  as  their  ana- 
tomical plane  is  moved  further  away  from  the  primary  reflex  centers  in 
the  brain  stem,  until  finally  in  the  cerebral  cortex  they  are  completely 
emancipated  from  control  by  any  particular  reflex  systems  but  instead 
they  themselves  may  regulate  all  bodily  activities. 

The  segmental  apparatus  is  often  called  the  hrain  stem.  It 
includes  practically  all  of  the  fish  brain  (Figs.  43  and  44)  except 
the  cerebellum,  for  in  these  animals  there  is  no  cerebral  cortex. 
If  in  the  human  brain  we  dissect  away  the  cerebral  cortex  and 
the  cerebellar  cortex  and  the  white  matter  immediately  con- 
nected therewith  we  have  the  form  shown  in  Fig.  45.  This  is 
the  human  brain  stem. 

Cortical  Dependencies. — It  should  be  noted  that  in  man  the  brain  stem 
is  not  exactly  synonymous  with  the  segmental  apparatus,  for  the  human 
brain  stem  includes  many  parts  which  have  been  developed  to  facilitate 
the  functional  interaction  between  the  cortex  and  the  phylogenetically 
older  reflex  centers.  These  structures  which  are  functionally  subsidiary 
to  the  cortex  are  called  cortical  dependencies  (see  pp.  236,  292).  The 
brain  stem  contains  similar  dependencies  of  the  cerebellum  (pons,  red 
nucleus,  etc.). 


ANATOMY    AND    SITT5DTVISION    OF    NERVOUS    SYSTEM 


123 


The  cerobelliun  appears  in  the  evolutionary  history  of  the 
vertebrate  ])rain  much  earhcr  than  tlie  eerel)ral  cortex;  its 


Nucleus  lenliformis 


Capsula  iBtema 
(pars  lenticulo-  ,, 
Cauda  ta) 


Traclus. 
olfactorius 

TFactus  opticus  '" 
lafundibulum-'' 

Hypophy-f  anterior  lobe 
sis  cerebri  \  posterior  lobe- — 


Capsula  interna  (pars  lenticulo-thalamica) 
Nucleus  caudatus 

Nucleus  amyudala;  (cut) 

Commissura  anterior 
Ftna  tcrminalis 

•^  '^r>  '"^  ^"  \  y 

^"S^^^^-^^  \^   ^Capsula  interna  (para 
sublenticularia) 
^Nucleus  caudatus 

X^^Thalamus 

Corpus  geniculatum 
laterale 

•^-O Corpus  pineale 

*  -j^^^-'-Cor.  geniculatum  mediale 
^^~Colliculus  superior 
J Colliculus  inferior 

^  ^>-^-Lemniscu3  lateralis 
Nervus  trochlearis 


Corpus  mamillare  /  / 
N   oculomotoriub 
BaMb  pedunculi 

Pon-'  X^ 

Nervus  trigeminus  (portio  major)  ''^^' 

Nervus  trigeminus  (portio  minor) ''    ___ 

N.  facialis'-^r^ 

N.  intermedius"^' -' 

N.  acusticus^,-' 

N.  abducens 

N.  glossopharj'ngeus-^  .- 

Nervus  vagus  ^    ,,-''''^ 

Pyiamis' 

Oliva- 

Fasciculus  circumolivaris  pyramidis" 


Brjchium  conjunctivum 

Brachium 
pontic 

Fossa  flocculi 

— Crus  flocculi 
^ — Nucleus  denta- 
,     .11  -,  )       tus  cerebelli 

Corpus  ponto-bulbare 

-Fasciculus  spinocerebellaris 
_ Nervus  spinalis 


Fig.  45. — Left  lateral  aspect  of  a  human  brain  from  which  the  cerebral 
hemisphere  (with  the  exception  of  the  corpus  striatum,  the  olfactory  bulb 
and  tract,  and  a  small  portion  of  the  cortex  adjacent  to  the  latter)  and  the 
cerebellum  (excepting  its  nucleus  dentatus)  have  been  removed.  The  brain 
stem  (segmental  apparatus;  palseencephalon)  includes  everything  here 
shown  with  the  exception  of  the  strip  of  cortex  above  the  tractus  olfac- 
torius and  the  nucleus  dentatus.  Within  its  substance,  however,  are  certain 
cortical  dependencies  (al^sent  in  the  lowest  vertebrates),  which  have  been 
developed  to  facilitate  communication  between  the  brain  stem  and  the 
cerebral  cortex.  The  chief  of  these  are  found  in  the  thalamus,  basis  pedunculi, 
and  pons.  Compare  this  figure  with  the  side  view  of  the  intact  brain.  Fig. 
54.     (Modified  from  Cunningham's  Anatomy.) 

functions  are  wholly  reflex  and  unconscious  (see  pp.  172,  204) 
and  are  concerned  chiefly  with  motor  coordination,  equilibra- 


124  IN'TBODUCTION   TO    NEUROLOGY 

tion,  and,  in  general,  the  orientation  of  the  body  and  its  mem- 
bers in  space.  Its  activities  are  of  the  invariable,  innate, 
structurally  predetermined  type  (see  pp.  22,  32,  84),  The 
cerebral  cortex,  on  the  other  hand,  is  the  organ  of  the  highest 
and  most  plastic  correlations,  which  are  in  large  measure 
individually  acquired.  It  attains  its  maximum  size  in  the 
human  brain. 

In  recognition  of  the  late  phylogenetic  origin  of  the  cerebral 
cortex  Edinger  has  called  the  brain  stem  (with  the  exception 
of  the  cortical  dependencies)  and  cerebellum  the  old  brain 
(palseencephalon),  and  the  cerebral  cortex  and  parts  of  the  brain 
developed  in  relation  therewith  the  new  brain  (neencephalon) . 

The  terminology  of  the  brain  is  in  great  confusion.  Most  of 
the  more  obvious  parts  were  named  before  their  functions  were 
known,  the  same  part  often  receiving  many  different  names, 
and  sometimes  the  same  name  being  applied  to  very  different 
parts.  To  remedy  this  situation  the  German  Anatomical 
Society  in  1895  published  an  official  list  of  anatomical  terms 
which  is  known  as  the  Basle  Nomina  Anatomica  (commonly 
abbreviated  as  B.  N.  A.).  Each  of  these  terms  has  a  clearly 
defined  significance  and  they  are  now  very  widely  used, 
though  many  anatomists  continue  to  use  some  older  and  un- 
official names.  The  B.  N.  A.  terms  or  their  English  equiva- 
lents are  used  in  this  work,  save  in  a  few  cases  which  are 
specifically  mentioned.  The  terminology  of  the  brain  is 
based  upon  the  embryological  researches  of  Professor  His, 
and  can  best  be  outlined  by  reviewing  the  form  of  the  human 
brain  at  a  few  selected  stages  of  development. 

The  B.  N.  A.  terminology  was  developed  with  exclusive  reference  to  the 
human  body.  The  names  of  many  parts  of  the  bodies  of  other  animals 
than  man  and  of  microscopic  structures  in  general  are  not  included.  The 
names  of  this  list  are  all  used  and  defined  in  W.  Krause's  Handbuch  der 
Anatomie  des  Menschen,  Leipzig,  1905,  and  in  most  of  the  recent  Ameri- 
can and  English  text-books  of  anatomy.  At  the  end  of  Krause's  book 
is  a  very  complete  list  of  synonyms,  including  most  of  the  anatomical 
terms  in  use  and  their  B.  N.  A.  equivalents.  The  B.  N.  A.  tables  of 
names  with  their  English  equivalents  are  given  in  Barker's  Anatomical 
Terminology  (1907),  and  Eycleshymer's  Anatomical  Names  (1917)  in- 
cludes a  full  reprint  "of  these  tables  with  a  translation  of  the  accom- 
panying annotations,  followed  by  biographical  sketches  of  anatomists 
prepared  by  Roy  L.  Moodie  and  by  a  full  index  of  synonyms. 

Following  the  example  of  many  other  recent  anatomists,  we  shall  in 


ANATOMY    AND    SUBDIVISION    OF   NERVOUS   SYSTEM 


125 


this  work  replace  the  B.  N.  A.  term  "anterior"  (on  the  front  or  belly  side) 
by  the  word  "ventral,"  and  the  B.  N.  A.  term  "posterior"  (on  the  back 
side)  by  the  woi'd  "dorsal."  The  head  end  of  the  body  will  be  referred 
to  as  the  "anterior"  or  "cephalic"  end;  the  other  end  of  the  body  as  the 
"posterior"  or  "caudal"  end.  The  terms  "upper"  or  "higher"  and 
"lower"  will  refer  to  the  relations  in  the  erect  human  body.  In  the 
nomenclature  of  the  medulla  oblongata  (see  p.  131)  and  of  the  thalamus 
(p.  182)  our  usage  departs  slightly  from  that  of  the  B.  N.  A.  Regard- 
ing the  naming  of  fiber  tracts  see  page  139. 

Figure  46  illustrates  the  form  of  the  brain  in  a  very  early 
human  embryo.     Its  tubular  form  is  very  evident,  and  in  the 


finkrior  heuropore 

iPalliunj  offeteticepha.ton 


Piencepbahn 


Corpui  striatum 


/Inferior  neuropore 


Mesencephalon 
Isihmui 


Mesencephalon 


Firiure  ponVme 
flcKure 


Opfic  recess 

Future  pontine 
Rhombencephalon      flexure 


Phombencephalon 


Fig.  46. — An  enlarged  model  of  the  brain  of  a  human  embryo  3.2  mm. 
long  (about  two  weeks  old).  The  outer  surface  is  shown  at  the  left,  and 
on  the  right  the  inner  surface  after  division  of  the  model  in  the  median 
plane.  The  Anterior  neuropore  marks  a  point  where  the  neural  tube  is 
still  open  to  the  surface  of  the  body.  The  Pallium  is  the  region  from  which 
the  cerebral  cortex  wdll  develop.  The  OjMc  recess  marks  the  portion  of  the 
lateral  wall  of  the  Diencephalon  from  which  the  hollow  Optic  vesicle  has 
evaginated.     (After  His,  from  Prentiss'  Embryology.) 


brain  the  diameter  of  the  tube  is  but  little  greater  than  that 
of  the  spinal  cord.  The  walls  are  thin  and  the  cavity  wide. 
In  a  shghtly  older  embryo  the  form  is  shown  in  Fig.  47,  and 
Fig.  48  illustrates  diagrammatically  the  median  section  of  an 
embryo  of  about  the  same  age  as  that  shown  in  Fig.  47,  upon 
which  the  regions  as  defined  by  the  B.  N.  A.  are  indicated. 


126 


INTRODUCTION    TO   NEUROLOGY 


fi/7esencepbalof 


Mvelencephalort 


Ceph.fU^ 


Metencepfiahn 

Corpus  sh-iatum 
Optic  Ticeis 
H^po  thalamus 


Mesencephalor, 


Cerebelluni 


Fig.  47. — Reconstruction  of  the  brain  of  a  6.9  mm.  human  embryo  (about 
four  weeks  old):  A,  Lateral  view;  B,  in  median  sagittal  section;  Ceph.flex., 
cephalic  flexure.      (After  His,  from  Prentiss'  Embryology.) 


Hypophysis  (anterior  lobe) 

Ventro-lateral   plae  ~~ 
Dorso-lateral  plate — 


Fig.  48. — Diagram  of  the  inner  surface  of  the  human  brain,  based  on  a 
specimen  of  about  the  same  age  as  shown  in  Fig.  47.  The  shaded  area  is 
the  ventro-lateral  plate  of  the  neural  tube,  giving  rise  to  the  motor  centers. 
Its  upper  boundary  is  marked  by  a  groove  on  the  ventricular  surface,  the 
sulcus  limitans,  which  separates  the  ventro-lateral  plate  from  a  dorso- 
lateral plate  (unshaded),  which  gives  rise  to  the  sensory  centers  and  chief 
correlation  centers.     (After  His,  from  Morris'  Anatomy.) 


ANATOMY    AND    SUBDIVISION    OF    NERVOUS    SYSTEM 


127 


„     .     ,      ,      ,  Cerebral  aqueduct 

Cerebral  pedunclti  !  Ueseiiupltalon 

IT  .  .L  I  .V:^ttiiiillih2-  (.Midbrain) 

Epilhahmus        \    .^ 

Thalamus 

Dienuphaton       V 

(JrUer-brain) 


Rhombencephalic 
isthmus 


Fig.  49. — Vertical  median  section  of  a  model  of  the  brain  of  a  human 
embryo  13.6  mm.  long:  1,  Optic  recess,  marking  the  attachment  of  the 
optic  vesicle;  2,  ridge  formed  by  the  optic  chiasma;  3,  optic  chiasma;  4,  in- 
fundibular recess.  The  limiting  sulcus  is  visible  in  the  model,  though  not 
named,  running  upward  from  the  optic  recess  between  the  thalamus  and 
the  hypothalamus.      (After  His,  from  Sobotta's  Atlas  of  Anatomy.) 


Epithaiamus  (Corpus  pineale) 

Metathalamus 
(Corpora  geniculata) 


Corpus  striatum. 


Corpora  quadrigcmlna 


Pedunculus  cerebri 


Ehinencepbalon 
Pars  optica  hypothalami 

Chiasma  opticum     , 
Hypophysis  ' 

Pars  mamillaris  hypothalami 

Pons  [Varoli] 


Metejjcephalon  4/    Cerebellum 


Fossa  rhomboidea 


Medulla  oblongata 


Fig.    50. — A  vertical  median  section  of  a  model  of  the  brain  of  a  human 
fetus  in  the  third  month.     (After  His,  from  Spaltcholz's  Atlas.) 


128 


INTRODUCTION  TO   NEUROLOGY 


Ehlnencephalon   . 

Eecessua  opticus 
Chiasma  opticum 


Eecessus  infundibul 

InfuDdibuluni 

Pedunculus  cerebri 


Epithalaiuua 
(Corpus  pineale) 

Corpora 
>  quadrigemina 


Veluta  medul- 
lare  anterius 


Pons  [Varoli] 


\h    olon  \^  Ventriculus  quartus 

wiyeien-r      ^i^^^w^,  oblongata 


Fig.   51. — Vertical  median  section  of  the  adult  human  brain.      (From  Spalte- 

holz's  Atlas.) 


SULCUS  CINGULl 
( margiiiat  portion) 


SUBPARIETAL  SULCUS 
PARIETO-OCCIPL 

TAL  FISSURE 
CALCARINB 
FISSURE 


CENTRAL  SULCUS  (ROLANDT) 

I  AfASSA  INTERMEDIA 

1       SULCUS  CINGULI 
f  {.suhfiontat  portion) 


Fig.  52.- 


ilESEMEPBALOV  I 

TUBER  OIICBUEVU 


nrpopnrsis 


',     \         \      ROStjtUM  OF  CORPUS  CALLOSUH 
\    \     \       ANTERIOR  PAROLFACTORY  SULCUS 
\    \         PAROLFACTORY  AREA  {BROCAS j^REA) 
\    ■  POSTERIOR  PAROLFACTORY  SULCUS 
'SUB'CALLOSAL  GYRUS  {PEDUNCLE  OF 
\  CORPUS  CALLOSUM) 

INFUNDIBULUil 


-Vertical  median  surface  of  the  adult  human  brain, 
from    Moms'   Anatomy.) 


(After  Toldt, 


ANATOMY    AND    SUBDIVISION    OF   NERVOUS    SYSTEM 


129 


The  brain  as  a  whole  is  the  encephalon,  and  its  chief  divisions 
are  indicated  by  prefixes  having  a  topographic  significance  ap- 
phed  to  this  word.  In  Fig.  48  the  ventral  part  of  the  neural 
tube  is  shaded  to  indicate  the  region  in  which  the  motor  centers 
of  the  adult  brain  are  found.  The  unshaded  part  of  the  figure 
indicates  the  region  devoted  to  the  primary  sensory  centers 


Optic  chiasma 


Infundibulum 
Left  corpus  mamillare 


Substantia  perforata 
posterior 

Pedunculiis  cerebri 


Olfactory  bulb 


Olfactory  tract 


Optic  nerve 


Substantia  perfora- 
ta anterior 

-Optic  tract 


Tuber  cinereum 


Abducens  nevre 


Hypoglossal  nerve 


Trochlear  nerve 


Glossopharyngeal  nerve 
Vagus  nerve 


Medulla  oblongata 
Medulla  spinalis  (cut) 


Accessory  nerve 
Hjfpoglossal  nen'e 


Fig.  53.- 


-Ventral    view    of    the    adult   human    brain.     Compare    Fig. 
(From    Cunningham's   Anatomy.) 


41. 


and  the  correlation  centers  related  to  them.  The  sensory  and 
motor  regions  are  separated  in  early  embryologic  stages  by  a 
longitudinal  limiting  sulcus  (the  sulcus  limitans).  Compari- 
son with  the  figures  of  later  stages  which  follow  shows  that 
the  suprasegmental  structures  are  developed  wholly  from  the 
sensory  region.  Figures  49  and  50  illustrate  later  stages  of 
development  and  Fig.  51  the  adult  brain  in  median  section. 

9 


130 


INTRODUCTION   TO   NEUROLOGY 


The  external  form  of  the  adult  brain  is  illustrated  also  in  Figs. 
52,  53,  54. 


PRECESTRAL  SULCUS 


CENTRAL  SULCUS  iROLANDI) 


SOXTAL  SULCUS 


horizontal 
Ramus  of  istbb- 
pabietal  sulcus 


SUPE- 
RIOR BI- 
TREMITZ 

[ OF 

PARIETO- 
OCCIPI- 
,       ,     ,     -        TALFIS- 
?•    I        1  1       ^^"^ 

occip.tales.  .^^^^^_ 

latcrales/  versb 
I  /  OCCIPI- 
I   i  TAL  SUL- 

CUS 


Fig.  54. — View  of  the  left  side  of  the  adult  human  brain.  Some  of  the 
principal  sulci  and  gyri  are  named.  The  lateral  cerebral  fissure  (sylvian 
fissure)  is  not  named;  it  lies  immediately  above  the  gyrus  temporalis  superior. 
(After  Toldt,  from  Morris'  Anatomy.) 

The  following  table  summarizes  the  relations  of  the  subdivi- 
sions of  the  brain  (the  ventricles  of  some  of  them  being  added 
in  parentheses),  to  which  a  few  comments  are  here  added: 

Rhombencephalon,  rhombic  brain  (fourth  ventricle). 
Myelencephalon,  medulla  oblongata. 
Metencephalon. 
Cerebellum. 
Pons. 
Isthmus  rhombencephali. 
Cerebrum. 

Mesencephalon,    midbrain    or    corpora    quadrigemina    and    cerebral 

peduncles  (aqueduct  of  Sylvius). 
Prosencephalon,  forebrain. 

Diencephalon,  betweenbrain  (third  ventricle). 
Hypothalamus. 
Thalamus. 
Metathalamus. 
Epithalamus. 
Telencephalon,  endbrain. 
Pars  optica  hypothalami. 
Hemisphseria,  cerebral  hemispheres  (lateral  ventricles). 


ANATOMY    AND    SUBDIVISION    OF   NP]RVOUS   SYSTEM  131 

The  isthmus  is  a  sharp  constriction  which  separates  the  brain 
into  two  major  divisions,  the  rhombencephalon  behind  and  the 
cerebrum  in  front.  In  the  B.  N.  A,  table  the  isthmus  is  re- 
garded as  a  transverse  segment  or  ring;  it  might  better  be 
regarded  simply  as  a  plane  of  separation  between  the  rhom- 
bencephalon and  cerebrum.  In  the  table  the  medulla  oblon- 
gata is  regarded  as  synonymous  with  myelencephalon,  that 
is,  the  region  between  the  pons  and  the  spinal  cord.  The 
older  usage,  which  is  still  widely  current,  regards  the  medulla 
oblongata  as  including  everything  between  the  isthmus  and 
the  spinal  cord  except  the  cerebellum  dorsally  and  the  fibers 
and  nuclei  of  the  pons  and  middle  peduncle  of  the  cerebellum 
ventrally.  This  is  the  old  or  segmental  part  of  the  rhom- 
bencephalon, and  the  cerebellum  and  pons  fibers  related  to 
it  are  added  to  this  primitive  medulla  oblongata.  The  older 
usage  is  preferable  to  the  B,  N.  A.  division  and  will  be  adopted 
here,  for  the  medulla  oblongata  as  here  defined  is  a  structural 
and  functional  unit,  whose  form  is  not  modified  in  those  ani- 
mals which  almost  totally  lack  the  cerebellum  and  its  middle 
peduncle.  As  indicated  on  page  158,  the  medulla  oblongata 
may  be  divided  on  functional  and  morphological  grounds 
into  an  upper  or  facial  part  and  a  lower  or  visceral  part  (the 
myelencephalon  of  the  B.  N.  A.). 

The  midbrain  (mesencephalon)  is  the  least  modified  part 
of  the  embryonic  neural  tube  in  the  adult  brain.  The  part 
above  the  ventricle  (corpora  quadrigemina)  contains  important 
correlation  centers  for  optic  and  auditory  reflexes  (p.  175) ; 
the  part  below  the  ventricle  (cerebral  peduncle)  contains 
primary  motor  centers  for  movement  of  the  eyeball  and  motor 
coordination  centers. 

The  betweenbrain  (diencephalon)  has  three  principal 
divisions:  (1)  below  is  the  hypothalamus;  (2)  above  is  the 
epithalamus;  (3)  between  these  is  the  thalamus  which  includes 
the  thalamus  and  metathalamus  of  the  table  (see  p.  182). 
The  hypothalamus  and  epithalamus  are  highly  developed  in 
the  lowest  vertebrates  and  are  related  to  the  olfactory  appara- 
tus; in  these  brains  the  thalamus  proper  is  very  small,  this 
part  increasing  in  size  in  the  higher  animals  parallel  with  the 
evolution  of  the   cerebral   cortex.     The   thalamus   proper  is 


132  INTRODUCTION  TO  NEUROLOGY 

really  a  sort  of  vestibule  to  the  cerebral  cortex;  all  nervous 
impulses  which  reach  the  cortex,  except  those  from  the  olfac- 
tory organs,  enter  it  through  the  thalamus.  The  endbrain 
(telencephalon)  includes  the  cerebral  hemispheres  and  a  very 
small  part  of  the  primitive  unmodified  neural  tube  to  which 
the  hemispheres  are  attached,  this  being  the  pars  optica 
hypothalami  of  the  table  or,  better,  the  telencephalon  medium. 

If  now  we  compare  this  subdivision  of  the  human  brain  with 
our  rough  functional  analysis  of  the  fish  brain  (p.  118),  we 
notice  that  the  ''ear  brain"  (acoustico-lateral  area),  "skin 
brain"  or  "face  brain"  (general  cutaneous  area),  and  "visceral 
brain"  (visceral  area)  are  all  contained  in  the  rhombencepha- 
lon, whose  segmental  or  stem  portion  is  made  up  of  these 
centers  and  the  corresponding  motor  centers.  The  same  rela- 
tions hold  in  the  human  brain,  and  in  both  cases  the  cere- 
bellum (and  in  man  the  pons  in  the  narrower  sense  in  which 
I  use  that  term)  is  added  as  a  suprasegmental  part.  In  both 
cases  the  "eye  brain"  includes  the  retina  of  the  eye,  the  optic 
nerve,  and  a  part  of  the  roof  of  the  midbrain.  In  the  fish 
a  very  small  part  of  the  thalamus  (not  indicated  on  Figs. 
43  and  44)  also  receives  fibers  from  the  optic  nerve.  In  man 
this  optic  part  of  the  thalamus  is  greatly  enlarged,  forming 
so  large  a  part  of  that  structure  in  fact  that  the  thalamus  as  a 
whole  is  often  called  the  optic  thalamus.  It  should  be  remem- 
bered, however,  that  even  in  man  the  optic  centers  comprise 
only  a  part  of  the  thalamus.  The  "nose  brain"  of  the  fish 
comprises  most  of  the  cerebral  hemispheres  (all  except  the 
small  "somatic  area"  of  Fig.  44),  and  all  of  the  epithalamus 
and  hypothalamus.  In  man  these  parts  remain  essentially  un- 
changed, but  the  "somatic  area"  of  the  hemisphere  has  greatly 
enlarged  to  form  the  large  corpus  striatum  and  the  enormous 
cerebral  cortex,  the  latter  forming  the  suprasegmental  appara- 
tus of  the  telencephalon,  and  greatly  modifying  the  form 
relations  of  all  adjacent  parts. 

The  details  of  the  development  of  the  brain  lie  outside  the 
scope  of  this  work,  as  also  do  the  anthropological  questions 
growing  out  of  the  statistical  study  of  brain  weights^  and 

1  The  weight  of  the  brain  is  exceedingly  variable,  even  in  a  homoge- 
neous population.  The  average  weight  of  the  normal  adult  European 
male  brain  is  commonly  stated  to  be  1360  grams  (48  oz.),  and  that  of  the 
female  1250  grams  (44  oz.). 


ANATOMY    AND    SUBDIVISION    OF    NERVOUS    SYSTEM  133 

measurements.  These  ;in(l  many  other  topics  of  fuiulaiiicntal 
importance  are  presented  in  a  very  interesting  way  in  Donald- 
son's book  on  The  Growth  of  the  Brain. 


The  Meninges. — The  central  nervous  system  is  enveloped  by  three 
membranes,  from  without  inward,  the  dura  mater,  arachnoid,  and  pia 
mater.     These  membranes  in  the  aggregate  are  called  meninges. 

The  dura  mater  of  the  brain  is  a  dense  fibrous  membrane  closely  ad- 
herent to  the  skull,  for  which  it  serves  also  as  the  inner  nourishing  mem- 
brane (periosteum).  These  two  functions  are  performed  by  separate 
parts  of  the  membrane  in  the  spinal  region,  where  the  bones  of  the  spinal 
column  are  provided  with  a  separate  inner  periosteal  covering  and  the 
spinal  cord  is  enveloped  by  a  distinct  cylindrical  membranous  dura  mater, 
the  two  being  separated  by  a  wide  epidural  space. 

A  fold  of  dura  mater  extends  downward  into  the  longitudinal  fissure 
between  the  two  cerebral  hemispheres  (falx  cerebri),  and  a  similar  fold 
extends  transversely  in  the  great  fissure  between  the  cerebrum  and  the 
cerebellum  (tentorium  cerebelli). 

The  arachnoid  is  a  very  delicate  membrane  adherent  to  the  dura  with 
a  far  less  compact  layer  adherent  less  closely  to  the  pia.  There  are  nu- 
merous subarachnoid  spaces  filled  with  fluid  between  the  outer  arachnoid 
and  the  pia. 

The  pia  mater  is  a  delicate  and  very  vascular  membrane  which  follows 
the  contour  of  the  brain  very  closely  and  from  which  the  greater  part  of 
the  internal  blood-vessels  of  the  brain  are  derived. 

The  Choroid  Plexuses. — In  the  development  of  the  brain  from  the  em- 
bryonic neural  tube  there  are  four  parts  of  the  brain  walls  which  remain 
thin  and  non-nervous.  Each  of  these  regions  is  known  as  an  epithelial 
plate  {lamina  epithelialis) .  One  of  these  is  seen  as  the  "Roof  plate" 
of  Fig.  70,  p.  167.  The  pia  mater  which  covers  these  epithelial  plates  is 
called  the  tela  chorioidea.  A  portion  of  each  of  the  four  epithelial  plates 
is  greatly  enlarged  and  thrust  into  the  underlying  brain  ventricle  in 
the  form  of  a  crumpled  fold.  The  outer  surface  of  these  folded  epithelial 
membranes  is  closely  covered  by  highly  vascular  pia  mater,  and  this 
portion  of  the  pia  is  called  a  choroid  plexus  {plexus  chorioideus) .  We 
have,  accordingly,  a  choroid  plexus  in  the  lateral  ventricle  of  each  cere- 
bral hemisphere  (Fig.  107,  p.  246),  a  choroid  plexus  of  the  third  ventricle 
(Fig.  79,  p.  181),  and  a  choroid  plexus  of  the  fourth  ventricle. 

The  cerebrospinal  fluid  is  a  clear  liquid  differing  in  chemical  composition 
from  the  lymph,  which  fills  the  ventricles  of  the  brain,  the  central  canal 
of  the  spinal  cord,  and  the  subarachnoid  spaces.  Some  of  the  subarach- 
noid spaces  are  greatly  enlarged  to  form  the  so-called  cisterns,  as  the 
cisterna  cerebello-medullaris  (or  magna)  between  the  medulla  oblongata 
and  the  cerebellum. 

The  functions  of  the  cerebrospinal  fluid  are  not  clearly  understood.  It 
seems  to  be  derived  from  both  the  choroid  plexuses  and  the  general 
brain  tissue.  There  are  no  definite  lymph  vessels  within  the  brain  or 
meninges  and  this  fluid  may  serve,  like  the  lymph  in  other  parts  of  the 
body,  to  carrj^  nutrient  and  waste  materials  concerned  in  the  me- 
tabolism of  the  brain  tissue  (see  Halliburton,  1916,  Weed,  1917,  and  the 
papers  there  cited). 


134  INTBODUCTION    TO    NEUROLOGY 

Sum7nary. — In  all  vertebrates  the  central  nervous  system  is 
fundamentally  a  hollow  dorsal  tube  in  which  the  primary  seg- 
mentation is  subordinated  to  the  development  of  important 
longitudinal  correlation  tracts  and  centers.  This  tube  is  en- 
larged at  the  front  end  to  form  the  brain.  The  vertebrate 
brain  may  be  divided  on  physiological  grounds  into  great 
divisions,  first  the  brain  stem,  or  primary  segmental  apparatus; 
and  second  the  cerebellum  and  cerebral  cortex,  or  supraseg- 
mental  apparatus.  The  brain  stem  and  cerebellum  are 
devoted  chiefly  to  reflex  and  instinctive  activities  and  con- 
stitute the  ''old  brain"  of  Edinger.  The  cerebral  cortex  is 
devoted  to  the  higher  associations  and  individually  acquired 
activities  and  is  called  the  ''new  brain"  by  Edinger.  No 
nervous  impulses  can  enter  the  cortex  without  first  passing 
through  the  reflex  centers  of  the  brain  stem. 

In  fishes  the  form  of  the  brain  is  shaped  almost  wholly  by  the 
development  of  the  reflex  centers,  and  here  these  mechanisms 
can  best  be  studied,  each  of  the  more  obvious  parts  of  the 
brain  being  dominated  by  a  single  system  of  sensori-motor 
reflex  circuits.  The  same  pattern  is  preserved  in  the  human 
brain,  but  much  distorted  by  the  addition  of  the  centers  of 
higher  correlation. 

The  terminology  of  the  brain  now  in  most  common  use  is 
based  on  its  embryological  development,  which  is  briefly 
reviewed. 

Literature 

Barker,  L.  F.     1907.     Anatomical  Terminology,  Philadelphia. 

Donaldson,  H.  H.  1899.  The  Growth  of  the  Brain,  a  Study  of  the 
Nervous  System  in  Relation  to  Education,  New  York. 

Edinger,  L.  1908.  The  Relations  of  Comparative  Anatomj^  to 
Comparative  Psychologj^,  Jour.  Comp.  Neur.,  voL  xviii,  pp.  437-457. 

Eycleshymer,  a.  C.  and  Shoemaker,  D.  M.  1917.  Anatomical 
Names,  especially  the  Basle  Nomina  Anatomica  ("B.  N.  A."),  with  Bio- 
graphical Sketches  by  R.  L.  Moodie,  New  York. 

Halliburton,  W.  D.  1916.  The  Possible  Functions  of  the  Cere- 
brospinal Fluid,  Brit.  Med.  Jour.,  vol.  ii,  p.  609. 

Herrick,  C.  Judson.  1910.  The  Morphology  of  the  Forebrain  in 
Amphibia  and  Reptiha,  Jour.  Comp.  Neur.,  vol.  xx,  pp.  413-547. 

Herrick,  C.  Judson  and  Crosby,  Elizabeth.  1918.  A  Laboratory 
Outline  of  Neurology,  Philadelphia. 

His,  W.  1895.  Die  anatomische  Nomenclatur:  Nomina  Anatomica, 
Archiv  f.  Anat.  und  Physiol.,  Anat.  Abt.,  Supplement-Band. 


ANATOMY    AND    SUBDIVISION    OF    NERVOUS    SYSTEM  135 

— .  1904.  Entwickelungs  des  menschlichen  Gehirns  wahrcnd  der 
ersten  Monate,  Leipzig. 

Johnston,  J.  B.  1906.  Tlie  Nervous  System  of  Vertebrates,  Phila- 
delphia. 

— .  1909.  The  Central  Nervous  System  of  Vertebrates,  Ergebnissc 
und  Fortschritte  der  Zoologie,  Bd.  2  Heft  2,  pp.  1-170. 

— .  1909.  The  Morphology  of  the  Forebrain  Vesicle  in  Vertebrates, 
Jour.  Comp.  Neur.,  vol.  xix,  pp.  457-539;  also  important  papers  on  the 
same  subject  in  later  volumes  of  The  Journal  of  Comparative  Neurology. 

Keibel,  F.,  and  Mall,  F.  P.  1912.  Manual  of  Human  Embryology, 
Philadelphia,  vol.  ii,  pp.  1-156. 

Krause,  W.  1905.  Handbuch  der  Anatomie  des  Menschen,  mit 
einem  Synonymenregister,  auf  Grundlage  der  neuen  Baseler  anatomis- 
chen  Nomenclatur,  Leipzig. 

Meyer,  A.  1898.  Critical  Review  of  the  Data  and  General  Methods 
and  Deductions  of  Modern  Neurologv,  Jour.  Comp.  Neur.,  vol.  viii, 
pp. 113-148,  249-313. 

Retzius,  G.     1896.     Das  Menschenhirn,  2  vols.,  Stockholm. 

Sherrington,  C.  S.  1906.  The  Integrative  Action  of  the  Nervous 
System,  New  York. 

Weed,  Lew^s,  H.  1917.  An  Anatomical  Consideration  of  the  Cere- 
brospinal Fluid,  Anat.  Rec,  vol.  xii,  pp.  461-496. 

— .  1917a.  The  Development  of  the  Cerebro-spinal  Spaces  in  Pig 
and  in  Man,  Contr.  to  Embryology,  No.  14,  Carnegie  Inst,  of  Washing- 
ton, Pub.  No.  225. 


CHAPTER  VIII 

THE  SPINAL  CORD  AND  ITS  NERVES 

The  spinal  cord  {medulla  spinalis)  is  the  least  modified  part 
of  the  embryonic  neural  tube,  and  the  spinal  nerves  constitute 
the  only  part  of  the  nervous  system  in  which  the  primitive  seg- 


Posterior  d 


Anterior  cutaneous  n. 
Fig.  55. — Diagram     of     a    typical    spinal    nerve    in    the    thoracic    region. 
The  spinal  column  and  the  muscles  are  shown  in  gray,  the  nerves  and  their 
ganglia  in  black.      (From  Gray's  Anatomy.) 

mental  pattern  is  clearly  preserved  in  the  adult  body  (see  p. 
122).  The  spinal  nerves  are  connected  with  th&  spinal  cord  in 
serial  order,  a  pair  of  nerves  for  each  vertebra  of  the  spinal 
column  (see  Fig.  41,  p.  115). 

136 


THE    SPINAL    CORD    AND    ITS    NERVES 


137 


Each  spinal  nerve  distributes  efferent  (motor)  fibers  to  the 
muscles  and  afferent  (sensory)  fibers  to  the  skin  and  deep 
tissues  of  its  appropriate  segment  of  the  body,  and  through  its 
connections  with  the  sympathetic  nervous  system  it  may  effect 
various  visceral  connections  (Figs.  55  and  56).  The  efferent 
fibers  leave  the  cord  through  the  ventral  roots  of  the  spinal 
nerves,  these  fibers  arising  from  cells  within  the  gray  matter  of 
the  cord,  and  the  afferent  fibers  enter  through  the  dorsal  roots, 


\     I     / 

^     ^    I  Cz 
\    \   I  (f 

Dorsal  column - 
Intermedio- 
lateral  column ' 


Ventral  column 


:h^ 


"Dorsal  root 


Ventral  root 


Visceral  muscle- 


\  1  ' 

ly'i: 

'  //C. 

o 

-^•'V    A 

r\ 

\     (-^  y  A 

mk 

-Preganglionic  fiber 
-Ramus  communicans 
-Sympathetic  ganglion 
-Postganglionic  fiber 


Mucous  membrane- 


Fig.  56. — Diagram  illustrating  the  composition  of  a  typical  spinal  nerve 
in  the  thoracic  region.  The  somatic  sensory  system  is  indicated  by  broken 
lines,  the  visceral  sensory  by  dotted  lines,  the  somatic  efferent  by  heavy 
continuous  lines,  the  visceral  efferent  by  lighter  continuous  lines.  (Compare 
Figs.  1  and  55.) 

these  fibers  arising  from  cell  bodies  of  the  spinal  ganglia  (see 
Fig.  1,  p.  26,  and  Figs.  55,  56).  The  fibers  of  the  spinal  nerves 
are  best  classified  in  accordance  with  the  same  physiological 
criteria  as  their  end-organs  (see  pp.  84-99,  and  compare  the 
cranial  nerves,  pp.  155-165)  into  somatic  afferent  (or  sensory), 
visceral  afferent  (or  sensory),  somatic  efferent  (or  motor), 
and  visceral  efferent  (or  motor)  systems  (Fig.  56). 

In  the  spinal  cord  the  originally  wide  cavity  of  the  embryonic 
neural  tube  (see  p.  125)  is  reduced  to  a  slender  central  canal 


138  INTRODUCTION  TO  NEUROLOGY 

and  the  walls  of  the  tube  are  thickened.  The  nerve-cells  retain 
their  primary  position  bordering  the  central  canal,  thus  form- 
ing a  mass  of  central  gray  matter  which  is  roughly  H -shaped  in 
cross-section.  This  gray  matter  on  each  side  is  accumulated 
in  the  form  of  two  massive  longitudinal  ridges,  a  dorsal  column 
(columna  dorsalis,  or  posterior  horn),  whose  neurons  receive 
terminals  of  the  sensory  fibers  of  the  dorsal  roots,  and  a  ventral 
column  (columna  ventralis,  or  anterior  horn)  whose  neurons 
give  rise  to  the  fibers  of  the  ventral  roots. 

The  white  matter  of  the  spinal  cord  is  superficial  to  the  gray 
and  is  made  up  of  sensory  and  motor  root  fibers  of  spinal 
nerves,  ascending  and  descending  correlation  fibers  putting 
different  parts  of  the  cord  into  functional  connection,  and 
longer  ascending  and  descending  tracts  by  which  the  spinal 
nerve-centers  are  connected  with  the  higher  association  centers 
of  the  brain.  In  general,  the  shorter  fibers  lie  near  to  the  cen- 
tral gray  and  the  longer  tracts  more  superficially. 

The  white  matter  which  borders  the  gray  in  the  spinal  cord 
is  more  or  less  mingled  with  nerve-cells  and  fine  unmyelinated 
endings,  and  thus  shows  under  low  powers  of  the  microscope  a 
reticulated  appearance.  This  is  the  reticular  formation  (pro- 
cessus reticularis)  of  the  cord  (see  pp.  69,  172,  and  Fig.  58). 
Immediately  surrounding  the  reticular  formation  and  partly 
embedded  within  it  are  myelinated  fibers  belonging  to  neurons 
intercalated  between  the  sensory  and  the  motor  roots,  which 
run  for  relatively  short  distances  in  an  ascending  or  descending 
direction  for  the  purpose  of  putting  all  levels  of  the  cord  into 
functional  connection  in  the  performance  of  the  more  complex 
spinal  reflexes.  These  fibers  form  the  deepest  layer  of  the 
white  matter  and  are  termed  the  fasciculi  proprii  (dorsalis, 
lateralis,  and  ventralis,  see  Fig.  59).  These  fascicles  are  also 
called  ground  bundles  and  fundamental  columns. 

In  the  narrow  space  between  the  ventral  fissure  and  the  cen- 
tral canal  (see  Fig.  58)  there  is  a  bundle  of  nerve-fibers  which 
cross  from  one  side  of  the  spinal  cord  to  the  other.  This  is  the 
ventral  commissure.  A  similar  but  smaller  dorsal  commissure 
crosses  immediately  above  the  central  canal. 

There  is  considerable  confusion  in  the  terminology  in  use  in  the  further 
analysis  of  the  spinal  white  matter,  and  the  usage  which  follows  differs 


THE    SPINAL    CORD    AND    ITS    NERVES 


139 


in  some  respects  from  most  of  the  classical  descriptions,  no  two  of  which 
agree  among  themselves.  We  shall  limit  the  application  of  the  term 
funiculus  to  the  three  major  divisions  of  the  white  matter  of  each  half 
of  the  spinal  cord,  viz.,  the  dorsal  funiculus  bounded  by  the  dorsal  fis- 
sure and  the  dorsal  root,  the  lateral  funiculus  lying  lietween  the  dorsal 
and  ventral  roots,  and  the  ventral  funiculus  between  the  ventral  root 
and  the  ventral  fissure  (Fig.  57). 

Each  funiculus  may  be  divided  in  a  purely  topographic  sense  into 
fasciculi,  or  collections  of  nerve-fibers  which  occupy  the  same  general 
region  in  the  cross-section  of  the  cord,  such  as  the  fasciculus  gracilis  of 
Goll  and  the  fasciculus  cuneatus  of  Burdach  (which  together  make  up 
the  greater  part  of  the  funiculus  dorsalis,  see  Figs.  67  and  59),  and  the 
superficial  ventro-lateral  fasciculus  of  Gowers  (including  among  other 
tracts  the  spino-tectal  tract  and  the  ventral  spino-cerebellar  tract  of 
Fig.  59).  These  fasciculi  are  usually  mixed  bundles  containing  tracts 
of  diverse  functional  types. 


Dorsal  root 

Dorsal  funiculus 

Dorsal  column 

Lateral  funiculus 

Lateral  oolumn 

Vent.al  column 

Ventral  funiculus 

Ventral  root 

Fig.  57. — Diagram  of  a  cross-section  through  one-half  of  the  spinal  cord 
to  illustrate  the  arrangement  of  the  funiculi  of  white  matter  and  the  columns 
of  gray  matter. 

The  true  physiological  units  of  the  spinal  white  matter  are  the  tracts, 
i.  e.,  collections  of  nerve-fibers  of  similar  functional  type  and  connections. 
Some  of  these  tracts  are  often  termed  fasciculi;  and,  like  the  other-tracts 
of  the  central  nervous  system,  they  are,  in  general,  named  in  accordance 
with  the  terminal  relations  of  their  fibers,  the  name  of  the  location  of 
their  cells  of  origin  preceding  that  of  their  place  of  discharge  in  a  hyphen- 
ated compound  word.  Thus,  the  tractus  cortico-spinalis  arises  from 
cells  of  the  cerebral  cortex  (p.  151),  and  terminates  in  the  spinal  cord, 
and  the  tractus  spino-cerebellaris  arises  in  the  spinal  cord  and  terminates 
in  the  cerebellum  (p.  142).  But,  as  already  stated,  there  is  no  uniformity 
in  the  nomenclature  of  these  tracts  and  no  two  authorities  agree  exactly 
in  the  terminology  adopted.  Moreover,  few  of  the  tracts  have  clearly 
defined  anatomical  limits,  in  most  cases  the  fibers  of  different  systems 
being  more  or  less  mingled. 

The  appearance  of  a  cross-section  through  the  spinal  cord  in 
the  lower  cervical  (neck)  region,  after  staining  so  as  to  reveal 


140 


INTRODUCTION   TO   NEUROLOGY 


the  arrangement  of  both  the  nerve-cells  and  the  nerve-fibers, 
is  seen  in  Fig.  58.  Figure  59  illustrates  diagrammatically  the 
arrangement  of  the  chief  fiber  tracts  in  the  same  region. 

The  spinal  cord  has  two  main  groups  of  functions,  first,  as  a 
system  of  reflex  centers  for  all  of  the  activities  of  the  trunk  and 
limbs;  second,  as  a  path  of  conduction  between  these  centers 
and  the  higher  correlation  centers  of  the  brain.     The  former 


Dorsal  median  septum 
Septuj" 
Dorsal  lateral  groove 


Dorsal  nerve  root 


Substantia  i 

Root-fibers  enterii 
matter 
Processus  reticu 


Central  cana 


Nucleus  from  wl 
motor    fiber? 
muscles   of  up 
limb  arise 

Ventral  white  co 
sure 


Ventral  nerve  root 

Ventral  median  fissure 


Fig.  58. — Cross-section  through  the  human  spinal  cord  at  the  level  of 
the  fifth  cervical  nerve,  stained  by  the  method  of  Weigert-Pal,  which  colors 
the  white  matter  dark  and  leaves  the  gray  matter  uncolored.  (From 
Cunningham's  Anatomy.) 


group  is  the  more  primitive,  and  there  is  evidence  that  in  the 
course  of  vertebrate  evolution  the  higher  centers,  especially  the 
cerebral  hemispheres,  exert  an  increasingly  greater  functional 
control  over  these  reflex  centers  (see  p.  312).  The  long  con- 
duction paths  between  the  spinal  cord  and  the  cerebral  hemi- 
spheres are,  accordingly,  much  larger  in  man  than  in  lower 
vertebrates.  It  is  impossible  in  the  space  at  our  disposal  to 
summarize  even  the  most  important  of  the  internal  connec- 


THE    SPINAL    CORD    AND    ITS    NERVES 


141 


tions  of  the  spinal  nerves;  we  can  only  select  a  few  typical 
illustrative  examples. 


Fasc.  gracilis' 

Fasc.  cuneatuB 

Fasc.  septo-marg. 

Fasc.  inter-fascic. 

Tr.  cortico-spin.  lat 

Tr.  rubro-spin. 

Nuc.  dorso-lat.- 

Nuc.  ventro-med  .. 

Nuc.  ventro-lat. 

Tr.  cortico-spin.  ven .. 

Tr.  olivo-spinalis 

Tr.  tecto-spinalis 

Tr.  vestibulo-spin. 

Radix  ventralis 


Radix  dorsalis 
Fasc.  dorso-lat. 
Tr.  spino-cereb.  dor. 
Columna  dorf^aiis 
Fasc.  proprius  dors. 
Fasc.  proprius  lat. 
Tr.  spino-cereb.  ven. 
Tr.  spino-thalam.  lat. 
Columna  ventralis 
Tr.  spino-tectalis 
Tr.  spino-thalam.  ven. 
Tr.  spino-olivaris 
Fasc.  proprius  ven. 
Fasc.  sulco-mare. 


Fig.  59. — Diagram  of  a  cross-section  through  the  human  spinal  cord  at 
the  level  of  the  fifth  cervical  nerve,  to  illustrate  the  arrangement  of  the  fiber 
tracts  in  the  white  matter  and  of  the  nerve-cells  in  the  gray  matter  of  the 
ventral  column.  On  the  right  side  the  area  occupied  by  the  dorsal  gray 
column  (posterior  horn)  is  stippled;  on  the  left  side  some  of  the  groups  of 
cells  of  the  ventral  gray  column  (anterior  horn)  are  indicated.  In  the  white 
matter  the  outlines  of  some  of  the  more  important  tracts  are  schematically 
indicated,  ascending  fibers  on  the  right  side  and  descending  fibers  on  the 
left.  The  same  area  of  white  matter  is  in  some  cases  shaded  on  both  sides 
of  the  figure.  This  indicates  that  ascending  and  descending  fibers  are 
mingled  in  these  regions.  A  list  of  the  tracts  here  illustrated  follows.  The 
names  here  employed  in  some  cases  differ  from  those  of  the  official  German 
Anatomical  Society  list  (see  p.  124),  the  B.  N.  A.  terms  here  being  italicized. 


Ascending  Tracts 

Fasciculus  gracilis  (column  of  GoU)  and  fasciculus  cuneatus  (column  of 
Burdach).  These  are  mixed  bundles  which  in  the  aggregate  make  up  the 
greater  part  of  the  dorsal  funiculus  (old  term,  posterior  columns).  They 
are  made  up  chiefly  of  the  ascending  branches  of  dorsal  root  fibers  (see 
Fig.  61),  those  in  the  gracilis  from  the  sacral,  lumbar,  and  lower  thoracic 
nerves  {S,  L,  T'5-12),  and  those  in  the  cuneatus  from  the  upper  thoracic 
and  cervical  nerves  (^1-4,  C),  as  indicated  in  the  figure.  These  fasciculi 
terminate  respectively  in  the  nuclei  of  the  fasciculus  gracilis  (clava)  and 
cuneatus  (tuberculum  cuneatum)  at  the  lower  end  of  the  medulla  ob- 
longata (cf.  Fig.  83),  and  conduct  chiefly  impulses  of  the  proprioceptive 
reflexes  and  those  concerned  with  sensations  of  posture,  spatial  discrimi- 
nation, and  the  coordination  of  movements  of  precision  (see  pp.  149, 
192). 

Fasciculus  dorso-lateralis  (tract  of  Lissauer,  Lissauer's  zone),  made  up 
chiefly  of  immyelinated  fibers  from  the  dorsal  roots,  together  with  myelin- 
ated correlation  fibers  of  the  fasciculus  proprius  sj-stem. 

Tractus  spino-cerebellaiis  dorsalis  (fasciculus  cerehello- spinalis,  direct 


142  INTEODUCTION  TO  NEUROLOGY 

cerebellar  tract,  Flechsig's  tract).  These  fibers  arise  from  the  neurons  of 
the  nucleus  dorsalis  (Clarke's  column  of  gray  matter  between  the  dorsal 
and  ventral  gray  columns  in  the  thoracic  region,  also  called  Stilling 's 
nucleus)  of  the  same  side  and  enter  the  cerebellum  by  way  of  its  inferior 
peduncle  {corpus  restiforme) . 

Tractus  spino-cerebellaris  ventralis  (part  of  Gowers'  tract,  or  the  fas- 
ciculus antero-lateralis  superficialis  of  the  B.  N.  A.).  These  fibers  also 
arise  from  the  nucleus  dorsalis  of  the  same  side  in  monkeys  (A.  N.  Bruce) 
in  the  lower  levels  of  the  spinal  cord  and  enter  the  cerebellum  by  way  of 
its  superior  peduncle  {brachiu7n  conjunctivum).  In  man  they  are  said 
to  arise  from  the  corresponding  region  of  the  cord  (though  the  nucleus 
dorsalis  is  not  here  recognizable),  and  many  of  them  are  beUeved  to 
decussate  in  the  ventral  commissure. 

The  spinal  lemniscus.  Under  this  name  are  included  several  tracts  to 
the  midbrain  and  thalamus.  These  fibers  arise  from  neurons  of  the  dor- 
sal gray  column,  cross  in  the  ventral  commissure,  and  ascend  in  the  lateral 
and  ventral  funiculi  of  the  opposite  side,  partly  superficially  mingled  with 
those  of  the  ventral  spino-cerebellar  tract  and  partly  deeper  in  the  fas- 
ciculus proprius.  This  system  of  fibers  includes  a  tractus  spino-tectalis 
to  the  roof  (tectum)  of  the  midbrain  and  a  tractus  spino-thalamicus  to  the 
ventral  and  lateral  nuclei  of  the  thalamus.  The  deeper  fibers  of  the  latter 
tract  are  arranged  in  two  groups,  the  tractus  spino-thalamicus  laterahs 
for  sensory  impulses  of  temperature  and  pain,  and  the  tractus  spino- 
thalamicus  ventralis  for  sensory  impulses  of  touch  and  pressure  (see  pp 
149,  189). 

Tractus  spino-olivaris,  fibers  arising  from  the  entire  length  of  the  spinal 
cord  and  terminating  in  the  inferior  olive  (Goldstein) . 

Descending  Tracts 

Tractus  cortico-spinahs  {fasciculus  cerehro-spinalis,  pyramidal  tract). 
This  system  of  fibers  conducts  voluntary  motor  impulses  from  the  pre- 
central  gyrus  of  the  cerebral  cortex  to  the  motor  centers  of  the  spinal 
cord.  It  divides  at  the  upper  end  of  the  spinal  cord  into  two  tracts,  the 
larger  division  immediately  crossing  through  the  decussation  of  the  pyra- 
mids to  the  opposite  side  of  the  spinal  cord,  where  it  becomes  the  trac- 
tus cortico-spinalis  lateralis  {fasciculus  cerehro-spinalis  lateralis,  lateral  or 
crossed  pyramidal  tract).  A  smaller  number  of  these  fibers  pass  down- 
ward into  the  spinal  cord  from  the  medulla  oblongata  without  decus- 
sation to  form  the  tractus  cortico-spinalis  ventralis  {fasciculus  cerehro- 
spinalis  anterior,  direct  pyramidal  tract,  column  of  Tlirck).  These 
fibers  cross  in  the  ventral  commissure  a  few  at  a  time  throughout  the 
upper  levels  of  the  cord,  and  finally  terminate  in  the  cervical  and  upper 
thoracic  regions  in  relation  with  the  motor  neurons  of  the  opposite  side. 
Both  parts  of  the  pyramidal  tract,  therefore,  decussate  before  their  fibers 
terminate  (see  p.  317). 

Tractus  rubro-spinalis  (tract  of  Monakow),  from  the  nucleus  ruber  of 
the  midbrain  to  the  spinal  cord,  for  thalamic  and  cerebellar  reflexes. 
They  cross  in  the  ventral  tegmental  decussation  (Fig.  75,  p.  176;. 

Tractus  olivo-spinalis  (Helwig's  bundle,  tractus  triangularis),  fibers 
descending  from  the  inferior  olive  of  the  medulla  oblongata  to  the  lower 
cervical  or  upper  thoracic  segments  of  the  spinal  cord. 


THE    SPINAL    CORD    AND    ITS    NERVES  143 

Tractus  tccto-spinalis  (predorsal  bundle,  tract  of  Lowentlial),  from  the 
roof  (tectum)  of  the  midbrain  to  the  spinal  cord,  chiefly  for  optic  re- 
flexes. Part  of  these  fibers  cross  in  tlie  dorsal  tefrmental  decussation, 
or  fountain  decussation  of  Mcynert  (Fig.  7.5,  p.  176). 

Tractus  yestibulo-spinalis,  from  the  primary  centers  of  the  vesti- 
bular nerve  in  the  medulla  oblongata  to  the  spinal  cord,  for  equilibratory 
reflexes. 

The  two  tracts  last  mentioned,  together  with  several  others,  compose 
the  fasciculus  marginalis  ventralis. 


The  Fasciculus  Proprius 

The  fasciculus  proprius  system  of  fibers  (also  called  ground  bundles, 
basis  bundles,  and  fundamental  bundles)  comprises  chieflj^  short  ascend- 
ing and  descending  fibers  arising  from  neurons  of  the  spinal  graj'  matter, 
for  intrinsic  spinal  reflexes.  In  general,  these  fibers  border  the  gray 
pattern,  but  in  the  dorsal  funiculus  some  are  aggregated  in  the  tractus 
septo-marginalis  and  the  fasciculus  interfascicularis  (comma  tract, 
tract  of  Schultze),  these  two  tracts  also  containing  descending  branches 
of  the  dorsal  root  fibers.  Some  fibers  of  the  fasciculus  proprius  ventralis 
lie  adjacent  to  the  ventral  fissure  and  are  termed  the  fasciculus  sulco- 
marginalis,  these  fibers  forming  the  direct  continuation  into  the  cord  of 
the  fasciculus  longitudinalis  medialis  (posterior  longitudinal  bundle) 
of  the  brain  (see  pp.  203,  235  ). 

The  sensory  nerves  which  enter  the  spinal  cord  come  either 
from  the  deep  tissues  or  from  the  skin,  and  both  of  these  types 
of  nerves  carry  fibers  of  very  diverse  functional  sorts  belonging 
to  the  somatic  sensory  group,  in  addition  to  visceral  fibers 
which  will  not  be  considered  here.  It  will  be  recalled  (see  pp. 
82,  84)  that  the  general  somatic  sensory  group  includes:  (1) 
proprioceptive  systems,  concerned  with  motor  coordination 
and  the  orientation  of  the  body  and  its  members  in  space 
(muscle  sense,  tendon  sense,  etc.),  and  (2)  exteroceptive  sys- 
tems, concerned  with  the  relations  of  the  body  to  its  environ- 
ment (touch,  temperature,  and  pain  sensibility).  The  first  of 
these  systems  is  sei'ved  chiefly  by  the  deep  nerves,  and  the 
second  chiefly  by  the  cutaneous  nerves,  though  this  is  not 
rigidly  true.  In  particular  it  should  be  noted  that,  even 
though  the  skin  be  completely  anesthetic,  the  nerves  of  deep 
sensibility  can  still  respond  not  only  to  their  proprioceptive 
functions,  but  also  to  the  ordinary  clinical  tests  for  the  extero- 
ceptive qualities  of  touch,  temperature,  and  pain,  though  with 
a  higher  threshold  than  in  the  case  of  the  cutaneous  end-organs 
of  these  senses. 


144 


INTRODUCTION    TO   NEUROLOGY 


Fig.  60. — Diagram  of  some  of  the  types  of  connection  between  the  sen- 
sory fibers  of  the  dorsal  root  and  the  motor  fibers  of  the  ventral  root  in  the 
spinal  cord  of  the  rabbit  (chiefly  after  the  researches  of  Philippson).  The 
visceral  connections  are  not  included. 

1.  Collateral  branches  of  the  dorsal  root  fibers  effect  synaptic  relations 
directly  with  dendrites  of  ventral  column  cells  of  the  same  or  the  opposite 
side. 

2.  Dendrites  of  ventral  column  cells  may  cross  to  the  opposite  side  and 
here  receive  terminals  of  dorsal  root  fibers. 

3.  A  correlation  neuron  may  be  intercalated  between  the  two  peripheral 
neurons  in  either  of  the  first  two  cases.  These  neurons  may  have  short 
axons  for  refiexeb  within  a  single  segment  (3a)  or  their  axons  may  pass  out 
into  the  white  matter  (fasciculus  proprius)  and  extend  for  longer  or  shorter 
distances  in  either  the  ascending  or  the  descending  direction  (or  after  branch- 
ing in  both  directions)  for  connections  with  more  remote  motor  centers  of 
the  same  or  the  opposite  side  {3b,  3c). 

4._The  root  fibers  arising  from  the  cells  of  the  ventral  column  themselves 
may  give  off  collateral  branches  which  return  to  the  gray  matter  and  there 
arborize  about  other  cells  of  the  ventral  column  belonging  to  different  func- 
tional groups  or  about  correlation  cells,  thus  facilitating  the  coordinated 
contraction  of  several  distinct  muscles  in  the  performance  of  some  complex 
reaction. 

The  neurons  of  the  dorsal  column  apparently  do  not  play  an  important 
role  as  intercalary  elements  in  the  simpler  spinal  reflexes.  The  axons  of 
these  cells  are  for  the  most  part  directed  upward,  after  decussating  in  the 
ventral  commissure,  and  are  chiefly  concerned  with  the  transmission  of 
nervous  impulses  from  the  spinal  cord  to  the  higher  correlation  centers  of 
the  brain. 


THK    SPINAL    CORD    AND    ITS    NERVES 


145 


Upon  entering  the  spinal  cord  all  of  these  functional  types 
of  fibers  effect  two  sorts  of  connections:  (1)  for  intrinsic  spinal 
reflexes,  and  (2)  for  the  transmission  of  their  impulses  upward 
to  the  higher  centers  of  the  brain.  We  shall  first  take  up  the 
intrinsic  connections. 

The  simplest  of  these  intrinsic  connections  is  the  direct 
motor  reflex  illustrated  by  Fig.  1  (p.  26),  but  there  are  many 
more  complex  forms  of  the  connection  between  the  dorsal  and 


-spinal    lemniscus 
correlation  neuronel 
funiculus    dorsalis 


correJation  neurone5 
(j   spg.4 


Fig.  61. — Diagram  of  the  spinal  cord  reflex  apparatus.  Some  of  the  con- 
nections of  a  single  afferent  neuron  from  the  skin  {d.r.2)  are  indicated:  d.?-. 2, 
dorsal  root  from  second  spinal  ganglion;  m,  muscles;  sp.g.l  to  sp.gA,  spinal 
ganglia;  v.r.V  to  v.rA,  ventral  roots. 


ventral  roots,  some  of  which  are  indicated  in  Figs.  60  and  61. 
In  general,  there  is  at  least  one  neuron  of  the  gray  matter  of  the 
spinal  cord  interpolated  between  the  dorsal  and  the  ventral 
root  neurons,  and  usually  there  is  a  complex  chain  of  such 
neurons.  As  may  be  observed  in  Fig.  61,  the  dorsal  root  fiber 
immediately  upon  entering  the  spinal  cord  divides  into  ascend- 
ing and  descending  branches,  and  secondary  branchlets  are 

10 


146  INTRODUCTION  TO  NEUROLOGY 

given  off  in  large  numbers  from  each  of  these,  so  that  a  single 
peripheral  sensory  neuron  may  discharge  its  nervous  impulses 
into  very  many  central  neurons  scattered  throughout  the  entire 
length  of  the  spinal  cord.  When  to  these  numerous  endings  we 
add  the  countless  ramifications  of  the  correlation  neurons,  it  is 
evident  that  even  in  the  spinal  cord,  which  is  the  simplest  part 
of  the  central  nervous  system,  there  are  reflex  mechanisms  of 
great  complexity.  Some  of  these  have  been  analyzed.  Sher- 
rington, in  his  Integrative  Action  of  the  Nervous  System,  has 
presented  a  very  clear  analysis  of  the  scratch  reflex  of  the  dog 
and  the  neural  mechanisms  involved.  The  mechanism  of  the 
locomotor  reflexes  has  been  studied  physiologically  and  histo- 
logically by  Steiner,  Philippson,  Polimanti,  Herrick  and  Cog- 
hill,  and  very  many  others. 

Our  most  precise  knowledge  of  the  arrangement  of  the  affer- 
ent and  efferent  myelinated  fibers  in  the  spinal  roots  has  been 
gained  by  the  application  of  Marchi's  method  (p.  50)  to  the 
study  of  degenerations  following  accidental  and  experimental 
injuries.  Nerve-fibers  which  have  been  cut  off  from  their  cells 
of  origin  degenerate  within  about  two  weeks  after  the  injury. 
It  is,  therefore,  possible  by  the  microscopic  study  of  a  divided 
nerve  with  Marchi's  method  (which  stains  only  the  degenerat- 
ing myelinated  fibers)  to  determine  on  which  side  of  the  injury 
are  the  cells  of  origin  from  which  these  fibers  arise. 

Figure  62  illustrates  the  effects  of  section  of  the  spinal  roots 
made  at  four  different  places.  In  the  first  case  section  of  the 
mixed  trunk  peripherally  of  the  union  of  the  dorsal  and  ventral 
roots  is  followed  by  degeneration  of  all  of  the  myelinated  fibers 
of  the  nerve-trunk,  showing  that  the  cell  bodies  of  all  of  these 
fibers  lie  centrally  of  the  injury.  In  the  second  case,  section  of 
the  ventral  root  close  to  the  spinal  cord  is  followed  by  degenera- 
tion of  all  the  fibers  of  this  root  without  disturbance  of  those 
of  the  dorsal  root,  showing  that  the  ventral  root  fibers  arise  as 
axons  of  cells  within  the  spinal  cord.  In  the  third  case  section 
of  the  dorsal  root  fibers  peripherally  of  the  ganglion  and  before 
their  union  with  those  of  the  ventral  root  results  in  the  degenera- 
tion of  all  of  the  fibers  of  the  mixed  nerve  which  arise  in  the 
spinal  ganglion  (sensory  fibers),  without  loss  of  any  motor 
fibers  from  the  ventral  root.     In  the  fourth  case  section  of  the 


THE    SPINAL    CORD    AND    ITS    NERVES 


147 


dorsal  root  on  the  central  side  of  the  ganglion  is  followed  by 
degeneration  of  all  myelinated  fibers  of  the  central  stump  of 
this  root,  but  not  of  the  peripheral  part  of  the  root  or  the  spinal 
ganglion.  This  shows  that  the  cells  of  origin  of  these  fibers  lie 
in  the  spinal  ganglion  and  not,  like  those  of  the  ventral  root, 


.  n 


m 


w 


Fig.  62. — Four  sketches  to  illustrate  the  degenerations  of  somatic  sensory 
and  motor  fibers  which  follow  section  of  spinal  nerve-roots  in  difTerent  places. 
Fibers  separated  from  their  cells  of  origin  will  degenerate,  as  shown  in  black 
(see  the  text,  p.  146). 


within  the  spinal  cord.  The  peripheral  processes  of  these 
ganglion  cells,  therefore,  are  dendrites,  and  the  centrallj'- 
directed  processes  which  compose  the  dorsal  roots  are  axons 
(cf.  Fig.  1,  p.  26,  and  Fig.  56,  p.  137). 

Another  useful  method  for  the  solution  of  problems  of  this 
character  is  the  study  of  the  fine  structure  of  the  cell  bodies  of 


148  INTRODUCTION  TO  NEUROLOGY 

the  neurons  after  such  experimental  lesions  as  those  just  de- 
scribed. Neurons  whose  peripheral  fibers  have  been  severed, 
thus  cutting  the  cell  body  off  from  its  usual  avenue  of  func- 
tional discharge,  within  a  few  days  thereafter  undergo  struc- 
tural changes,  chief  of  which  is  chromatolysis,  or  the  solution 
and  disappearance  of  the  Nissl  bodies  (see  p.  47).  Thus,  after 
cutting  a  ventral  spinal  root  (Fig.  62,  II),  a  microscopic  exami- 
nation of  the  spinal  cord  will  show  the  chromatolysis  effect 
(see  Fig.  13,  p.  51)  in  every  neuron  in  the  ventral  gray  column 
which  gives  rise  to  a  fiber  of  this  root,  while  all  of  the  other 
neurons  will  remain  normal. 

Physiological  experiments  upon  men  and  other  animals 
where  such  injuries  have  taken  place  give  the  necessary  control 
to  confirm  the  proof  that  efferent  fibers  leave  the  spinal  cord 
through  the  ventral  roots  and  afferent  fibers  enter  through  the 
dorsal  roots,  for  the  loss  of  ventral  roots  results  in  a  motor 
paralysis  of  the  muscles  supplied  by  them,  while  the  destruc- 
tion of  dorsal  roots  results  in  the  loss  of  superficial  and  deep 
sensibility  in  the  regions  innervated,  with  no  loss  of  motor 
function  save  for  the  imperfect  coordination  resulting  from  the 
loss  of  the  sensory  control  through  the  proprioceptive  system 
(ataxia) . 

By  the  use  of  these  and  other  methods,  together  with  careful 
dissections,  the  peripheral  functional  connections  of  all  of  the 
spinal  nerves  have  been  determined,  as  given  in  Reid's  chart 
,(p.  69)  and  other  similar  tables. 

Turning  now  to  the  conduction  paths  between  the  spinal 
cord  and  the  brain,  we  notice  first  that  the  reactions  involved 
here  may  be  performed  either  reflexly  or  consciously.  In  the 
latter  case  a  connection  with  the  cerebral  cortex  is  to  be  ex- 
pected; in  the  former  case  an  infinite  variety  of  reflex  connec- 
tions within  the  brain  stem  is  possible. 

The  sensory  or  ascending  fibers  which  pass  between  the 
spinal  cord  and  the  brain  may  be  classified  as  follows: 

I.  Proprioceptive  systems: 

1.  To  the  cerebellum  (unconscious). 

2.  To  the  brain  stem  (unconscious). 

3.  To  the  thalamus  and  cerebral  cortex  (sensations  of  posture  and 

spatial  adjustment). 


THE    SPINAL    CORD    AND"  ITS    NERVES  149 

II.  Exteroceptive  systems: 

1.  To  the  brain  stem  (unconscious). 

2.  To    the    thalamus  and    cerebral  cortex   (sensations  of  touch, 

temperature,  and  pain). 

I.  Proprioceptive  Systems. — As  soon  as  the  afferent  fibers  of 
the  spinal  nerves  have  entered  the  spinal  cord  they  are  im- 
mediately segregated  into  proprioceptive  and  exteroceptive 
groups,  as  suggested  by  the  analysis  above  (see  Figs.  63,  64,  81, 
and  83).  The  proprioceptive  fibers  take  quite  different  courses, 
depending  upon  whether  they  are  directed  into  the  cerebellar 
path  or  into  the  path  to  the  brain  stem  and  cerebral  cortex. 
Some  terminals  of  this  system  end  in  the  gray  matter  between 
the  dorsal  and  ventral  columns  (the  nucleus  dorsalis  of  Clarke, 
or  Clarke's  column,  and  adjacent  regions),  whose  neurons  send 
their  axons  into  the  dorsal  and  ventral  spino-cerebellar  tracts 
and  finally  into  the  cerebellum.  The  cerebellum  is  the  great 
center  of  motor  coordination,  and  these  spino-cerebellar  tracts 
are  two  only  out  of  a  larger  number  of  paths  by  which  afferent 
spinal  impulses  may  be  discharged  into  it  (see  p.  206). 

The  remaining  proprioceptive  fibers  of  the  spinal  roots  are 
directed  upward  in  the  dorsal  funiculus,  of  which  they  form  the 
larger  part.  At  the  point  where  the  spinal  cord  passes  over 
into  the  medulla  oblongata  they  terminate,  and  after  a  synapse 
here  the  neurons  of  the  second  order  carry  the  impulse  across  to 
the  opposite  side  of  the  brain  and  upward  toward  the  thalamus 
in  a  tract  known  as  the  medial  lemniscus  or  fillet  (Fig.  64). 
After  another  synapse  here,  a  final  neuron  may  carry  the  nerv- 
ous impulse  forward  to  the  cerebral  cortex.  This  medial  lem- 
niscus system  is  largely  concerned  with  unconscious  motor 
adjustments  involving  the  muscles  of  the  trunk  and  limbs. 
Disturbance  of  its  functions  produces  motor  incoordination 
(ataxia),  but  not  necessarily  any  great  loss  of  exteroceptive 
sensations.  So  far  as  its  fanctions  come  into  consciousness, 
they  are  recognized  as  sensations  of  position,  spatial  locahza- 
tion,  and  motor  control. 

II.  Exteroceptive  Systems. — The  central  course  of  the 
exteroceptive  fibers  of  the  spinal  nerves  is  quite  different  from 
that  just  described.  Almost  immediately  after  entering  the 
spinal  cord  these  fibers  terminate  among  the  neurons  of  the 


150 


iNTRODtJCTlON   TO   NEUROLOGY 


dorsal  gray  column.  After  a  synapse  here  the  fibers  of  the 
second  order  cross  to  the  opposite  side  of  the  spinal  cord,  and 
here  turn  and  ascend  in  the  white  matter  of  the  lateral  and 
ventral  funiculi,  where  they  form  the  spinal  lemniscus,  or 
tractus  spino-thalamicus.  Some  fibers  of  the  spinal  lemniscus 
ascend  throughout  the  entire  length  of  the  spinal  cord,  medulla 


'Fasciculus  gracilis    "j 
'Fasciculus  cuneatus  j 


proprioceptive 


Dorsal  spino-cere- 
bellar  tract  (pro- 
prioceptive) 

Nucleus  dorsalis  of 
Clarke 

Ventral  spino-cere- 
bellar  tract  (pro- 
prioceptive) 

Spinal  lemniscus 
(exteroceptive  for 
pain,    heat,    and 
cold) 

Spinal  lemniscus 
(exteroceptive  for 
touch    and   pres- 
sure) 

Fig.  63. — Diagram  to  illustrate  the  terminations  within  the  spinal  cord 
of  some  of  the  types  of  somatic  sensory  fibers  and  their  secondary  paths. 
The  central  connections  of  root  fibers  1,  2,  and  5  provide  for  proprioceptive 
responses;  those  of  fibers  3  and  4,  for  exteroceptive  responses.  Root  fiber 
1  terminates  in  the  nucleus  of  the  fasciculus  cuneatus  of  the  same  side  at 
the  upper  end  of  the  spinal  cord  and  conveys  impulses  of  muscular  sensi- 
bility, sense  of  passive  position  and  movement,  and  of  spatial  discrimina- 
tion. Root  fiber  2  terminates  in  the  nucleus  dorsalis  of  Clarke  (Clarke's 
column)  and  root  fiber  5  in  the  same  nucleus  or  adjacent  parts  of  the  gray 
substance.  These  fibers  call  forth  unconscious  cerebellar  activity  underly- 
ing the  coordination  and  reflex  tone  of  the  muscles.  Root  fibers  3  and  4 
terminate  in  the  dorsal  gray  column  and  convey  exteroceptive  impulses. 
Fiber  3  typifies  all  fibers  which  carry  sensibility  of  pain,  heat,  and  cold; 
fiber  4,  those  which  carry  sensibility  of  touch  and  pressure  (see  p.  142, 
Spinal  lemniscus). 

oblongata,  and  midbrain,  to  end  in  the  thalamus.  In  the 
upper  part  of  their  course  these  fibers  accompany  those  of  the 
medial  lemniscus  already  described. 

Collateral  connections  are  effected  between  the  ascending 
fibers  of  the  spinal  lemniscus  and  the  various  motor  nuclei  of 
the  brain  for  different  cranial  reflexes,  such  as  turning  the  eyes 
in  response  to  a  cutaneous  stimulation  on  the  hand.     But  their 


THE    SPINAL    CORD    AND    ITS    NERVES  151 

final  terminus  is  in  the  thalamus,  and  after  a  synapse  here  the 
nervous  impulse  may  be  carried  forward  to  the  cerebral  cortex 
by  neurons  of  the  third  order.  The  spinal  lemniscus  system  is 
the  chief  ascending  pathway  for  nervous  impulses  giving  rise  to 
consciousness  of  touch,  temperature,  and  pain  from  the  trunk 
and  limbs.  There  is  a  similar  but  anatomically  distinct  path- 
way to  the  thalamus  for  cutaneous  sensibility  from  the  head, 
which  is  called  the  trigeminal  lemniscus  (see  p.  197  and  Figs. 
64,  77,  81). 

Within  the  spinal  cord  the  nerve-fibers  of  sensibility  to  pres- 
sure, pain,  and  temperature  run  in  three  distinct  tracts  of  the 
spinal  lemniscus  (the  pain  and  temperature  tracts  very  close 
together,  see  Figs.  59,  63,  and  81),  so  that  it  occasionally  hap- 
pens that  one  may  be  destroyed  by  accident  or  disease  without 
affecting  the  other  two.  Thus,  at  the  level  of  the  fifth  cervical 
vertebra  the  destruction  of  the  pathway  for  touch  and  pressure 
(tractus  spino-thalamicus  ventralis  of  Fig.  59)  would  result  in 
the  total  loss  of  both  cutaneous  and  deep  sensibility  to  pressure 
over  the  whole  of  the  opposite  side  of  the  body  below  the  level 
of  the  injury,  but  there  would  be  no  disturbance  of  either  tem- 
perature or  pain  sensibility.  Similarly,  by  an  injury  of  the 
tractus  spino-thalamicus  lateralis,  pain  or  temperature  sensi- 
bility might  be  lost  with  no  disturbance  of  pressure  sense.  (For 
the  description  of  a  case  of  this  sort  see  p.  190.) 

Such  combinations  of  symptoms  as  just  described  could  not 
occur  from  any  form  of  injury  to  the  peripheral  nerves,  for  in 
these  nerves  the  various  kinds  of  fibers  are  all  mingled  in  the 
larger  trunks,  so  that  one  functional  component  cannot  be  in- 
jured without  involvement  of  the  others  also.  And  at  the 
first  division  of  these  trunks  into  deep  and  superficial  branches 
each  branch  also  carries  all  or  nearly  all  of  the  functional 
systems  (see  pp.  84-90). 

The  return  pathway  for  motor  nervous  impulses  from  the 
cerebral  cortex  is  the  cortico-spinal  tract  or  pyramidal  tract 
(Fig.  64),  whose  fibers  descend  without  interruption  from  the 
precentral  gyrus  of  the  cerebral  cortex  (see  p.  316)  to  the  spinal 
cord,  where  they  form  the  lateral  and  ventral  cortico-spinal 
tracts  (Fig.  59).  The  various  reflex  centers  of  the  brain  stem 
also  send  motor  fibers  downward  into  the  cord  for  the  excita- 


152 


INTRODUCTION    TO    NEUROLOGY 


cerebral 


cortex 


trigeminal   lemniscus 
sKin 


ventral  pyramidal 
tract 


nucleus  of  dorsal 

funiculus 


clorsol  funiculus 
ateral  pyramidal  tract 
spinal  ganglion 
sKin 


Fig.  64. — Diagram  of  the  chief  conuections  between  the  spinal  cord  and 
the  cerebral  cortex.  The  spinal  lemniscus  complex  carries  the  ascending 
exteroceptive  systems  (touch,  temperature,  and  pain) ;  the  dorsal  funiculus 
and  medial  lemniscus  complex  carries  chiefly  ascending  proprioceptive  sys- 
tems (a  nerve  of  muscle  sense  is  the  only  member  of  this  group  included 
in  the  drawing).  The  diagram  also  includes  the  sensory  path  from  the  skin 
of  the  head  to  the  cerebral  cortex  through  the  V  cranial  nerve  (trigeminus) 
and  the  trigeminal  lemniscus  (p.  171).  The  pyramidal  tract  (tractus  cor- 
tico-spinalis)  is  the  common  descending  motor  path  for  both  exteroceptive 
and  proprioceptive  nervous  impulses  from  the  cerebral  cortex. 


THE    SPINAL    CORD    AND    ITS    NERVES  153 

tion  of  movements  of  the  trunk  and  limbs.  The  tecto-spinal 
tract  (Fig.  59)  is  such  a  path,  leading  from.the  optic  and  acous- 
tic centers  of  the  midbrain,  as  is  also  the  vestibulo-spinal  tract, 
leading  from  the  vestibular  nuclei  of  the  medulla  oblongata 
(p.  194,  Fig.  83,  neuron  16). 

Summary. — The  spinal  nerves  are  segmentally  arranged  and 
are  named  after  the  vertebrae  adjacent  to  which  they  emerge 
from  the  spinal  canal  of  the  vertebral  column.  Each  nerve 
arises  by  a  series  of  dorsal  rootlets  afferent  in  function  and  a 
series  of  ventral  rootlets  efferent  in  function.  Most  of  the  gray 
matter  of  the  spinal  cord  is  massed  in  two  longitudinal  columns 
on  each  side,  for  somatic  sensory  and  somatic  motor  functions 
respectively.  These  are  separated  by  an  intermediate  region 
containing  the  visceral  sensory  and  motor  centers  and  various 
correlation  neurons.  The  wliite  matter  of  the  cord  is  super- 
ficial to  the  gray  and  contains  myelinated  fibers  for  various 
kinds  of  correlation,  besides  root-fibers  of  the  spinal  nerves. 
The  white  matter  is  divided  topographically  into  funiculi  and 
fasciculi  and  physiologically  into  tracts.  The  latter  are  the 
really  significant  units  in  the  analysis  of  the  cord.  Peripher- 
ally, the  spinal  nerves  divide  into  deep  and  superficial  branches, 
and  each  of  these  contains  various  functional  systems  of 
fibers.  As  soon  as  the  peripheral  nerve-fibers  have  entered 
into  the  spinal  cord  they  are  segregated  into  proprioceptive  and 
exteroceptive  groups,  and  each  of  these  again  into  particular 
functional  tracts.  There  are  connections  for  local  spinal 
reflexes,  reflexes  of  the  brain  stem  and  cerebellum,  and  for  the 
cerebral  cortex.  The  spino-cerebellar  tracts  and  the  dorsal 
funiculi  are  proprioceptive  in  function,  and  the  spinal  lemniscus 
carries  spino-thalamic  tracts  of  the  systems  of  touch,  tempera- 
ture, and  pain  sensibility  for  the  cerebral  cortex.  (See  further 
in  Chapter  XL) 

Literature 

On  the  Functional  Analysis  of  the  Spinal  Nerves,  see  Chapter  IX  antl 
bibliographies  on  pages  100,  101,  174. 

Barker,  L.  F.  1901.  The  Nervous  System  and  Its  Constituent  Neu- 
rones, New  Yoik. 

Brouwer,  B.  1915.  Die  biologische  Bedeutung  der  Derniatonierie. 
Beitrag  zur  Kenntnis  der  Segmentalanatomie  und  der  Sensibilitiitsleitung 
im  Riickenmark  und  in  der  Medulla  Oblongata,  Folia  Neuro-biologica, 
Bd.  9,  pp.  225-336. 


154  INTRODUCTION   TO    NEUROLOGY 

Bruce,  A.     1901.     A  Topographic  Atlas  of  the  Spinal  Cord,  London. 

Bruce,  A,  N.  1910.  The  Tract  of  Gowers,  Quart.  Journ.  Exp. 
Physiol.,  vol.  iii,  pp.  391-407. 

Head,  H.,  Rivers,  W.  H.  R.,  and  Sherren,  J.  1905.  The  Afferent 
Nervous  System  from  a  New  Aspect,  Brain,  vol.  xxviii,  pp.  99-115. 

Head,  H.,  and  Thompson,  T.  1906.  The  Grouping  of  the  Afferent 
Impulses  Within  the  Spinal  Cord,  Brain,  vol.  xxix,  p.  537. 

Herrick,  C.  Judson,  and  Coghill,  G.  E.  1915.  The  Development 
of  Reflex  Mechanisms  in  Amblystoma,  Jour.  Comp.  Neur.,  vol.  xxv, 
pp.  65-85. 

Philippson,  M.  1905.  L'autonomie  et  la  centrahsation  dans  le 
systeme  nerveux  des  animaux,  Paris. 

PoLiMANTi,  O.  1911.  Contributi  alia  fisiologia  del  sistema  nervoso 
centrale  e  del  movimento  dei  pesci,  Zool.  Jahrb.,  Abt.  f.  Zool.  u.  Physiol., 
Bd.  30,  pp.  473-716. 

Rivers,  W.  H.  R.,  and  Head,  H.  1908.  A  Human  Experiment  in 
Nerve  Division,  Brain,  vol.  xxxi,  p.  323. 

Sherrington,  C.  S.  1906.  The  Integrative  Action  of  the  Nervous 
System,  New  York. 

Steiner,  J.  1885.  Die  Functionen  des  Centralnervensj^stems  und 
ihre  Phylogenese.  I.  Abteilung.  Untersuchungen  iiber  die  Physiologie 
des  Froschhirns,  Braunschweig. 

— .     1888.     Idem.  II.  Abteilung,  Die  Fische. 

— .  1900.  Idem.  IV.  Abteilung,  ReptiUen-Rlickenmarksreflexe, 
Vermischtes. 

— .  1886.  Ueber  das  Centralnervensystem  der  griinen  Eidechse  nebst 
weiteren  Untersuchungen  iiber  das  des  Haifisches,  Sitzb.  k.  Akad.  Wiss., 
Berlin,  p.  541. 


CHAPTER  IX 
THE  MEDULLA  OBLONGATA  AND  CEREBELLUM 

The  brain  contains  a  series  of  primary  sensory  and  motor 
centers  related  to  the  cranial  nerves  and  to  their  respective 
end-organs  (see  p.  117),  the  correlation  mechanism  which 
serves  to  connect  these  sensori-motor  centers  in  working  reflex 
systems,  and  an  extensive  system  of  conduction  pathways 
between  the  brain  and  spinal  cord  and  between  the  various 
correlation  centers  of  the  brain  itself  to  serve  the  more  complex 
systems  of  correlation  and  integration. 

The  brain  is  divided  into  two  principal  parts  by  a  constric- 
tion in  front  of  the  cerebellum  and  pons,  the  isthmus  (see  p. 
131).  Above  this  level  lies  the  cerebrum  and  below  it  the 
rhombencephalon,  comprising  the  medulla  oblongata  or 
bulb  and  the  cerebellum.  The  medulla  oblongata  contains 
the  primary  centers  concerned  with  most  of  the  simpler  cere- 
bral reflexes,  especially  those  of  the  visceral,  general  cutaneous, 
auditory,  and  proprioceptive  systems  (see  pp.  118-121). 
The  cerebellum  is  a  suprasegmental  apparatus  developed 
phylogenetically  and  embryologically  out  of  the  more  primitive 
bulbar  nuclei  of  the  vestibular  nerve,  i.  e.,  out  of  theacoustico- 
lateral  area  of  fishes  (Figs.  43  and  44,  pp.  119,  120,  and  Fig. 
68;  see  also  Herrick,  1914a). 

The  olfactory  nerve  (I  pair),  the  so-called  optic  nerve  (II 
pair),  and  the  auditory  nerve  (VIII  pair)  are  special  sensory 
nerves,  whose  central  connections  will  be  described  more  in 
detail  below.  The  remaining  nine  pairs  of  cranial  nerves  of 
the  human  body  may  be  briefly  summarized  as  follows: 

The  oculomotor  nerve  (III  pair),  ti'ochlear  nerve  (IV  pair),  and  ab- 
ducens  (VI  pair)  contain  the  somatic  motor  fibers  and  fibers  of  muscle 
sense  related  to  the  six  muscles  which  move  the  eyeball.  The  III  pair 
also  contains  visceral  motor  fibers  for  the  ciliary  ganglion,  from  which 
are  innervated  the  muscles  of  the  ciliary  process  and  iris  within  the  eye- 
ball, i.  e.,  the  muscles  of  accommodation  and  those  which  contract  the 

155 


156  INTEODUCTION  TO  NEUROLOGY 

pupil.  The  trigeminal  nerve  (V  pair)  supplies  general  sensibility  to  the 
skin  and  deep  tissues  of  the  face  and  the  motor  innervation  of  the  muscles 
of  mastication.  The  facial  nerve  (VII  pair)  innervates  the  taste-buds 
of  the  anterior  two-thirds  of  the  tongue  (special  visceral  sensory  fibers), 
the  sublingual  and  submaxillary  sahvary  glands  (general  visceral  efferent 
fibers),  and  the  muscles  related  with  the  hyoid  bone  and  the  superficial 
facial  muscles  or  muscles  of  facial  expression,  these  two  groups  of  muscles 
belonging  to  the  series  of  special  visceral  muscles  (p.  98).  The  glosso- 
pharyngeal nerve  (IX  pair)  supplies  fibers  to  the  taste-buds  on  the  pos- 
terior third  of  the  tongue  (special  visceral  sensory),  also  general  sensibility 
to  this  region,  motor  fibers  for  the  stylopharyngeus  muscle  (special 
visceral  motor),  and  excito-glandular  fibers  for  the  parotid  salivary  gland 
(general  visceral  efferent).  It  also  cooperates  with  the  vagus  nerve  in 
innervating  the  skin  about  the  external  auditory  canal  (by  the  auricular 
branch  of  the  vagus).  The  vagus  nei-ve  (X  pair)  is  very  complex.  In 
addition  to  the  general  somatic  sensory  fibers  of  the  auricular  branch, 
which  have  just  been  mentioned,  it  contains  general  visceral  sensory 
fibers  from  the  pharynx,  lungs,  stomach,  and  other  abdominal  viscera, 
and  visceral  efi'erent  fibers  of  several  sorts  to_  the  pharjmx,  esophagus, 
stomach,  intestines,  lungs,  heart,  and  arteries.  The  peripheral  and 
central  courses  of  most  of  these  functional  systems  have  been  accurately 
determined,  but  are  far  too  complex  for  summary  here.  The  accessory 
nerve  (XI  pair)  contains  two  parts:  (1)  the  bulbar  part,  which  should 
be  regarded  as  nothing  other  than  detached  filaments  of  the  vagus,  for 
all  of  these  fibers  peripherally  join  vagus  branches,  (2)  the  spinal  part, 
which  arises  by  numerous  rootlets  from  the  upper  levels  of  the  spinal 
cord  and  participates  in  the  innervation  of  two  of  the  muscles  of  the 
shoulder  (the  trapezius  and  sternocleidomastoid  muscles).  The  human 
hypoglossus  nerve  (XII  pair)  is  a  modified  derivative  of  the  first  spinal 
nerve  of  lower  vertebrates.  It  has  lost  its  sensory  fibers  and  innervates 
a  special  part  of  the  tongue  musculature.  All  of  the  nerves  of  the  pre- 
ceding list  except  the  I,  II,  III,  and  IV  pairs  connect  with  the  medulla 
oblongata. 

For  the  details  of  the  arrangement  of  the  cranial  nerves 
and  their  cerebral  centers  the  larger  manuals  of  neurology- 
must  be  consulted.  Here  we  have  space  for  only  a  brief 
summary  of  some  of  the  general  principles  which  may  assist 
in  organizing  these  intricate  anatomical  facts  in  more  com- 
prehensible form. 

The  cranial  nerves  are  usually  described  in  our  text-books 
as  if  they  were  segmental  units  like  the  spinal  nerves  (see  p. 
136).  This  was,  in  fact,  the  primitive  condition  which  is  still 
fairly  obvious  in  the  motor  roots  and  nuclei  (see  Fig.  71) ;  but 
in  all  vertebrate  animals  this  segmental  pattern  has  been 
greatly  modified  in  such  a  way  as  to  facilitate  the  discharge 
into  the  brain  of  all  sensory  fibers  of  like  physiological  type  into 
a  single  center.     The  sensory  roots  and  centers,  accordingly, 


THE    MEDULLA    OBLONGATA    AND    CEREBELLUM  157 

do  not  show  so  clearly  the  primitive  segmental  pattern  (Fig. 
71).  These  physiological  systems  of  fibers  of  hke  functional 
type  are,  therefore,  the  most  useful  units  of  structure  in  the 
cranial  nerves.  Each  cranial  nerve  may  contain  several  of 
these  functional  systems,  and  no  two  pairs  of  cranial  nerves 
have  the  same  composition.  The  components  of  the  cranial 
nerves,  like  those  of  the  spinal  nerves  (p.  137),  are  named  in 
accordance  with  the  same  physiological  criteria  as  their  end- 
organs  (see  pp.  84-99). 

A  functional  system  may  be  defined  as  the  sum  of  all  the 
neurons  in  the  body  which  possess  certain  physiological  and 
anatomical  characters  in  common  so  that  they  may  react  in  a 
common  mode.  Morphologically,  each  system  of  peripheral 
nerves  is  defined  by  the  terminal  relations  of  its  fibers — by  the 
organs  with  which  they  are  related  peripherally  and  by  the 
centers  in  which  the  fibers  arise  or  terminate.  A  single  periph- 
eral nerve  may  contain  several  of  these  systems.  It  becomes 
necessary,  therefore,  to  analyze  the  root  complex  of  each  pair  of 
spinal  and  cranial  nerves  into  its  components,  and  to  trace  not 
only  the  central  connections  of  these  components  within  the 
spinal  cord  and  brain,  but  also  their  peripheral  courses  as  well. 
In  other  words,  the  description  of  any  given  nerve  or  ramus  is 
not  complete  when  we  have  given  its  point  of  origin  from  the 
nerve-trunk,  root,  or  ganglion,  the  details  of  its  devious  courses, 
and  the  exact  points  where  the  several  ramuli  terminate.  In 
addition  to  this  it  is  necessary  to  learn  what  functional  systems 
are  represented  in  each  ramus  and  the  precise  central  and 
peripheral  relations  of  each  system. 

The  functional  systems  of  peripheral  nerve-fibers  are  so 
arranged  in  the  cranial  nerves  as  to  suggest  a  rough  grouping 
of  the  nerves  and  of  their  related  primary  centers  in  terms  of 
the  peripheral  apparatus  innervated.  Thus  in  man,  as  in 
fishes  (pp.  120,  132),  the  olfactory  organ  is  related  by  means 
of  the  olfactory  nerve  with  special  olfactory  centers  which  are 
described  in  Chapter  XV. 

The  eyes  are  similarly  connected  by  the  II  pair  of  nerves 
with  optic  centers  (Chapter  XIV),  with  which  are  intimately 
related  the  eye-muscle  nerves  (III,  IV  and  VI  pairs).  The 
skin  and  muscles  of  the  face  and  the  facial  skeleton  are  inner- 


158  INTRODUCTION   TO   NEUROLOGY 

vated  chiefly  by  the  V  and  VII  pairs,  and  the  part  of  the  brain 
with  which  these  nerves  connect  may  be  called  the  facial 
part  of  the  medulla  oblongata  (see  p.  131).  Next  follows  the 
VIII  pair  of  nerves,  connecting  the  internal  ear  with  the 
highly  specialized  vestibular  and  cochlear  nuclei.  Finally,  the 
lower  part  of  the  medulla  oblongata  (myelencephalon  of  the 
B.  N.  A.,  p.  130)  is  dominated  by  the  visceral  connections  of 
the  IX,  X  and  XI  pairs,  and  this  region  might  well  be  called 
the  visceral  part  of  the  medulla  oblongata. 

The  Doctrine  of  Nerve  Components. — The  physiological  analysis  of  the 
spinal  nerves  is  diagrammatically  indicated  in  Fig.  56  (p.  137),  this 
pattern  being  segmentally  repeated  with  minor  variations  throughout 
the  length  of  the  spinal  cord  (Fig.  41,  p.  115). 

The  functional  distinction  between  the  dorsal  (sensory)  and  the  ventral 
(motor)  roots  of  the  spinal  nerves  is  known  as  Bell's  law.  In  reality, 
however,  Sir  Charles  Bell's  analysis  was  more  like  our  current  conception 
of  the  composition  of  the  spinal  and  cranial  nerves  than  is  commonly 
recognized;  for  he  identified  not  only  the  somatic  sensory  and  somatic 
motor  components  but  also  the  visceral  components.  The  experimental 
researches  of  Bell  more  than  a  century  ago  were  carried  out  in  a  com- 
parative spirit  and  laid  the  foundation  for  the  analysis  of  the  functional 
composition  of  the  nerves  and  their  spinal  and  cerebral  centers.  An 
excellent  popular  account  of  these  researches  will  be  found  in  the  intro- 
ductory pages  of  Bell's  Bridgewater  Treatise  (1885,  pp.  xi-xxxv).  See 
also  Bell  (1811)  and  (1844).  Many  years  later  Gaskell  (1886,  1889) 
gave  a  more  explicit  account  of  the  visceral  components  which,  however, 
differs  considerably  from  that  now  in  use. 

The  knowledge  of  the  composition  of  the  cranial  nerves  was  long 
retarded  by  persistent  attempts  to  analyze  them  in  accordance  with  the 
analogy  of  a  supposed  simple  spinal  pattern.  The  typical  spinal  nerve 
according  to  the  present  conception  contains  two  great  groups  of  fibers, 
the  somatic  and  the  visceral,  each  with  afferent  and  efferent  subdivisions. 
The  somatic  group  is  concerned  with  the  adjustment  of  the  body_  to  the 
outside  world;  the  visceral  group  is  concerned  with  the  mechanisms  of 
circulation,  nutrition,  etc.,  and  its  connections  are  made  through  the 
sympathetic  nervous  system  (p.  249). 

The  somatic  efferent  fibers  pass  directly  from  their  cell  bodies  in  the 
ventral  gray  column  of  the  spinal  cord  through  the  ventral  roots  to  end 
upon  the  fibers  of  the  skeletal  muscles.  The  somatic  afferent  fibers  are 
processes  of  neurons  of  the  spinal  gangha.  The  somatic  motor  and 
sensory  fibers  of  the  cranial  nerves  are  organized  in  essentially  the  same 
way  as  just  described. 

The  visceral  fibers  of  the  spinal  nerves  are  chiefly  efferent  m  function. 
These  efferent  fibers  arise  from  the  intermedio-lateral  column  of  gray  in 
the  spinal  cord.  They  do  not  reach  their  terminal  organs  (smooth 
muscles,  glands,  etc.)  directly,  but  always  end  in  some  sympathetic 
ganglion,  with  whose  cells  they  effect  functional  connection.  The  im- 
pulse is  then  carried  on  to  the  peripheral  organ  by  axons  of  these  sym- 
pathetic neurons.     The  first  of  these  elements,  whose  cell  body  lies  within 


THE  MEDULLA  OBLONGATA  AND  CEREBELLUM     159 

the  cord,  is  called  the  preganglionic  neuron;  the  second  is  the  post- 
ganglionic neuron. 

The  visceral  sensory  fibers  of  the  spinal  nerves  are  relatively  few  in 
number.  Some  such  fibers  arise  from  cell  bodies  of  the  spinal  ganglia, 
whose  peripheral  processes  distribute  through  the  sympathetic  nervous 
system  to  mucous  surfaces,  etc.,  and  whose  central  processes  enter  the 
spinal  cord  through  tlie  dorsal  roots.  Other  sensory  fibers  are  supposed 
to  arise  from  cell  bodies  in  the  sympathetic  ganglia,  but  of  these  we  have 
less  positive  information. 

The  cranial  nerves  exhiliit  a  much  more  complex  and  diversified  pattern 
than  do  the  spinals.  Their  primary  segmentation  is  obscure  and  there 
is  still  some  difference  of  opinion  as  to  the  segmental  relations  of  the 
twelve  pairs  as  now  commonly  enumerated.  These  twelve  pairs  are 
convenient  anatomical  units,  but  for  physiological  and  clinical  purposes  a 
much  more  useful  unit  is  the  functional  system  as  defined  above. 

The  analysis  of  these  functional  systems  has  been  successfully  ac- 
complished by  physiological  experiment,  microscopic  reconstructions 
from  serial  sections,  and  other  methods  in  representatives  of  many 
groups  of  vertebrates,  and  the  general  pattern  is  found  to  be  tolerably 
uniform  throughout  (see  the  works  by  Johnston  (1906  and  1909)  cited 
in  the  appended  bibliography  for  summaries  of  some  of  this  literature). 

Each  of  the  four  primary  divisions  of  the  spinal  nerves 
(somatic  sensory  and  motor,  visceral  sensory  and  motor,  see 
p.  137)  is  represented  in  the  head  region  in  the  same  primitive 
unspecialized  form  as  seen  in  the  spinals,  and  also  by  special- 
ized systems  found  only  in  one  or  more  cranial  nerves.  This 
gives  eight  groups  of  functional  systems  represented  in  the 
cranial  nerves,   as  follows: 

1.  General  somatic  afferent  nerves,  supplying  (1)  general  exteroceptive 
sensibility  to  the  skin  and  the  underlying  tissues,  and  (2)  deep  pro- 
prioceptive sensibility  to  the  muscles,  tendons,  etc.  Type  1  is  repre- 
sented in  the  V,  IX,  and  X  nerves,  and  in  some  lower  vertebrates  in  the 

VII  nerve  also  (there  is  some  clinical  evidence  for  its  presence  in  the  VII 
nerve  of  man) ;  type  2  is  represented  in  the  III,  IV,  V,  VI  nerves  and 
probably  in  some  of  the  others  also. 

2.  Special  somatic  afferent  nerves,  for  the  innervation  of  highly  differ- 
entiated sense  organs.  Here  belong  in  the  exteroceptive  series  the  coch- 
lear branch,  and  in  the  proprioceptive  series  the  vestibular  branch  of  the 

VIII  pair.  The  lateral  line  nerves  of  fishes  belong  here,  and  probably  the 
visual  organ  connected  with  the  II  pair  in  all  vertebrates  (though  the  so- 
called  optic  nerve  is  not  a  true  nerve,  see  p.  228). 

3.  General  somatic  efferent  nerves,  supplying  the  general  skeletal 
musculature  of  the  body.  In  fishes  this  system  is  represented  in  several 
cranial  nerves  in  addition  to  the  spinalis,  but  in  man  it  is  lost  in  the  cranial 
nerves,  imless,  as  some  believe,  a  part  of  the  fibers  of  the  XI  pair  liclong 
here. 

4.  Special  somatic  efferent  nerves,  supplying  two  groups  of  highly 
specialized  somatic  muscles,  namely,  the  external  eye  muscles  and  a  part 
of  the  tongue  muscles.  They  arise  from  a  ventro-medial  series  of  motor 
nuclei  and  are  represented  in  the  III,  IV,  VI,  and  XII  pairs. 


160 


INTRODUCTION   TO    NEUROLOGY 


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162  INTRODUCTION  TO  NEUROLOGY 

5.  General  visceral  afferent  nerves,  innervating  visceral  mucous  sur- 
faces without  highly  differentiated  sense  organs.  They  distribute  through 
the  sympathetic  nervous  system  and  are  represented  "in  the  VII,  IX,  and 
X  pairs  and  perhaps  in  some  others. 

6.  Special  visceral  afferent  nerves,  for  the  innervation  of  specialized 
sense  organs  serving  the  senses  of  taste  and  smell.  The  gustatory  fibers 
are  represented  in  the  VII,  IX,  and  X  pairs.  The  olfactory  nerve  (I 
pair)  is  probably  a  more  highly  differentiated  member  of  this  group 
(see  pp.  97  and  239). 

7.  General  visceral  efferent  nerves,  for  unstriped  involuntary  visceral 
muscles,  heart  muscle,  glands,  etc.,  distributing  through  the  sj'mpathetic 
nervous  system.  These  fibers  (preganglionic  fibers  of  Langley,  p.  256)  are 
present  in  the  III,  VII,  IX,  X,  and  XI  pairs. 

8.  Special  visceral  efferent  nerves,  supplying  highly  specialized  striated 
muscles  of  a  different  origin  (both  embryologically  and  phylogenetically) 
from  the  striated  trunk  muscles.  These  muscles  are  connected  with  the 
visceral  or  facial  skeleton  of  the  head  and  are  derived  from  the  gill 
muscles  of  fishes.  These  nerves  in  the  adult  body  resemble  those  of  the 
somatic  motor  system,  save  that  they  arise  from  a  different  series  of 
motor  nuclei  in  the  brain  (the  ventro-lateral  motor  column).  They  have 
no  connection  with  the  sympathetic  nervous  system  and  are  represented 
in  the  V,  VII,  IX,  X,  and  XI  pairs. 

In  the  preceding  Table  of  Nerve  Components  (pages  160,  161)  the 
several  cranial  nerves  are  analyzed  and  compared  with  a  typical  spinal 
nerve. 

The  various  functional  systems  of  the  head  tend  to  be  con- 
centrated in  one  or  a  few  cranial  nerves  for  ease  of  central 
correlation,  and  even  in  case  a  given  system  is  represented  in 
several  nerves,  the  fibers  of  this  system  may  converge  within 
the  brain  to  connect  with  a  compact  center.  This  is  well 
illustrated  by  the  gustatory  and  acoustico-lateral  systems  of 
the  cranial  nerves  of  the  fish,  Menidia,  as  shown  in  Fig.  65. 
Here  the  gustatory  system  (indicated  by  cross-hatching)  is 
present  in  the  VII,  IX,  and  X  cranial  nerves,  and  all  of  these 
fibers,  together  with  other  visceral  fibers,  converge  within  the 
brain  to  enter  the  visceral  sensory  area  in  the  vagal  lobe 
{lob.  X.).  Similarly,  the  lateral  line  components  of  the  VII 
and  X  nerves  and  the  VIII  (printed  in  solid  black)  converge 
to  enter  the  acoustico-lateral  area  (formerly  called  the  tuber- 
culum  acusticum,  t.a.).  The  general  cutaneous  fibers  enter 
by  the  V  and  X  nerves,  and  all  of  these  fibers  enter  the  spinal 
V   tract    (sp.V.). 

In  the  paragraphs  which  follow  the  chief  central  connections  (terminal 
nuclei  of  the  sensory  systems  and  nuclei  of  origin  of  the  motor  systems, 
see  p.  116)  of  some  of  the  cranial  nerve  components  are  summarized  (see 


THE    MEDULLA    OBLONGATA    AND    CEREBELLUM 


163 


Fig.  71).     For  the  (letails  of  these  connections  th(!  hir^er  text-books  of 
neurology  should  be  consulted. 


Fig.  65. — A  diagram,  of  the  sensory  components  of  the  cranial  nerves  of  a 
tish,  Menidia.  The  brain  is  outlined  as  seen  from  the  right  side  with  heavy 
black  lines.  The  general  cutaneous  nerves  (somatic  sensory)  are  outlined 
with  finer  lines  (unshaded),  and  all  of  these  fibers  are  seen  to  enter  a  longi- 
tudinal tract  within  the  brain,  the  spinal  trigeminal  tract  (sp.V.).  The 
special  somatic  sensory  (acoustic  and  lateral  line)  nerves  (black)  converge 
within  the  brain  to  a  special  center,  the  acoustico-lateral  area  (t.a.).  The 
visceral  sensory  fibers  (cross-hatched)  likewise  all  converge  to  a  special  center, 
the  lobus  vagi  (lob.X.). 

Reference  letters:  b.c.l  to  b.c.5,  gill  clefts;  br.g.X.,  branchial  ganglia  of 
X  nerve;  cil.g.,  ciliary  ganglion;  d.l.g.VII.,  dorsal  lateral  line  ganglion  of  VII 
nerve;  f.c,  fasciculus  solitarius;  gen.g.VII.,  geniculate  ganglion  of  VII 
nerve;  IX.,  glossopharyngeal  nerve;  jug.g.,  jugular  ganglion  of  X  nerve; 
lob.X.,  lobus  vagi  (visceral  sensory  area);  7i./.,* olfactory  nerve;  n.II.,  optic 
nerve;  n.II  I.,  oculomotor  nerve;  o.pr.,  ramus  ophthalmicus  profundus;  pal., 
palatine  branch  of  VII  nerve;  r.cut.dors.X.,  dorsal  cutaneous  branch  of  X 
nerve;  r.intest.X.,  intestinal  branch  of  X  nerve;  r.lat.ac,  ramus  lateralis  ac- 
cessorius  of  VII  nerve;  r.lat.X.,  lateral  line  branch  of  X  nerve;  r.oph.sup.V. 
-\-VII.,  superficial  ophthalmic  branch  of  V  and  VII  nerves;  r.ot.,  ramus 
oticus;  r.st.X.,  supratemporal  branch  of  X  nerve;  r.VII.p-t.,  pretrematic 
branch  of  VII  nerve;  sp.V.,  spinal  trigeminal  tract;  t.a.,  acoustico-lateral 
area;  t.hrn.,  hyomandibular  trunk;  t.inf.,  infraorbital  trunk;  VIII.,  auditory 
nerve;  v.l.g.VII.,  ventral  lateral  line  ganglion  of  VII  nerve. 


1.  General  Cutaneous  System  (part  of  the  general  somatic  afferent, 
represented  in  the  V,  IX,  and  X  nerves). — Chief  sensory  V  nucleus  and 
spinal  V  nucleus,  or  gelatinous  substance  of  Rolando  of  the  medulla 
oblongata. 


164  INTRODUCTION   TO    NEUROLOGY 

2.  Special  Somatic  Afferent  Systems. — (1 )  Vestibular  nuclei ;  (2)  cochlear 
nuclei ;  (3)  optic  tectum  in  the  colliculus  superior,  optic  part  of  the  thala- 
mus (lateral  geniculate  body  and  pulvinar). 

3.  General  Somatic  Efferent  System. — Not  represented  in  the  human 
cranial  nerves. 

4.  Special  Somatic  Efferent  Systems  (III,  IV,  VI,  and  XII  nerves). — 
A  series  of  ventral  motor  nuclei  in  the  midbrain  and  medulla  oblongata. 

5  and  6.  General  and  Special  Visceral  Afferent  Systems  (VII,  IX,  and  X 
nerves). — All  of  the  fibers  concerned  with  general  visceral  sensibility  and 
taste  enter  a  single  longitudinal  tract,  the  fasciculus  solitarius,  and  ter- 
minate in  the  nucleus  which  accompanies  this  fasciculus.  (The  olfactory 
nerve  and  its  cerebral  centers  probably  should  also  be  included  here. ) 

7.  General  Visceral  Efferent  Systems  (III,  VII,  IX,  X,  and  XI  nerves). — 
These  are  preganglionic  fibers  of  the  sympathetic  system  and  arise  from 
laterally  placed  nuclei  (except  that  of  the  III  nerve,  which  is  joined  to  the 
ventral  somatic  motor  nucleus). 

8.  Special  Visceral  Efferent  Systems  (V,  VII,  IX,  X,  and  XI  nerves). — 
A  series  of  lateral  motor  nuclei  of  the  medulla  oblongata. 

The  spinal  nerves,  as  we  have  seen,  enter  the  spinal  cord  by  a 
series  of  segmentally  arranged  roots!     Within  the  spinal  cord, 


Somatic  sensory  column 

Visceral  sensory  column 
Visceral  motor  column 

Somatic  motor  column 


Dorsal  funiculus 
Dorsal  column 
Lateral  column 
Ventral  column 


Fig.  66. — Diagrammatic  transverse  section  through  the  spinal  cord  of  a 
fish  (Menidia)  to  illustrate  the  relations  of  the  functional  columns  of  the 
gray  matter  to  the  nerve  roots.  The  relations  of  the  visceral  sensory 
component  are  problematical,  and  fibers  of  the  visceral  motor  component 
probably  emerge  with  the  dorsal  root,  as  well  as  with  the  ventral  root, 
though  only  the  latter  are  included  in  the  diagram. 

however,  their  components  are  rearranged  in  longitudinal  col- 
umns which  cut  across  and  obscure  the  primary  segmentation. 
The  sensory  root-fibers  and  their  terminal  gray  centers  occupy 
the  dorsal  part  of  the  spinal  cord  and  the  motor  roots  and  their 
centers  the  ventral  part  (Figs.  66  and  67).  In  the  brain  the 
same  arrangement  prevails,  the  sensory  centers  lying  dorsal  to 
the  motor.  In  the  cranial  nerves,  moreover,  the  four  primary 
groups  of  functional  systems  of  the  peripheral  nerves  are  more 
clearly  differentiated  than  in  the  spinal  nerves,  and  from  this 
it  follows  that  their  primary  centers  are  correspondingly  highly 


THE    MEDULLA    OBLONGATA    AND    CEREBELLUM  165 

developed  and  distinct.  The  medulla  oblongata,  in  fact,  is 
divided  into  four  longitudinal  columns  related  respectively  to 
the  great  primary  groups  of  functional  systems.  In  fishes, 
where  the  amount  of  correlation  tissue  is  less  than  in  man,  these 
four  primary  columns  appear  as  well-defined  ridges  in  the  wall 
of  the  fourth  ventricle  (see  pp.  118-121). 

An  enlarged  view  of  the  medulla  oblongata  of  the  sturgeon, 
which  is  very  similar  to  that  of  the  dogfish,  is  seen  in  Fig.  68, 
which  also  illustrates  the  arrangements  of  the  primary  sensory 
and  motors  centers  in  cross-section  at  several  different  levels. 


Somatic  sensory  column  — 

Visceral  sensory  column  -J 

Visceral  motor  column  _l 

Somatic  motor  column  — 


Fig.  67. — Diagrammatic  transverse  section  through  the  human  spinal 
cord.  Compare  Figs.  56  to  59  and  note  the  relatively  greater  size  of  the 
dorsal  gray  columns  and  dorsal  funiculi  in  man  than  in  the  fish  (Fig.  66). 
This  is  correlated  with  the  greater  importance  in  man  of  the  ascending 
connections  between  the  cord  and  the  brain  (see  p.  140). 

Figure  69  shows  a  cross-section  through  the  medulla  oblongata 
in  the  region  of  the  vagus  nerve  in  another  fish,  the  sea-robin. 
In  all  of  these  cases  the  four  principal  functional  sj^stems  (see 
pp.  81  and  84-99)  are  arranged  in  longitudinal  columns  from 
the  dorsal  to  the  ventral  surface  in  the  order :  somatic  sensory, 
visceral  sensory,  visceral  motor,  and  somatic  motor  centers,  as 
indicated  diagrammatically  on  the  left  side  of  Fig.  69.  The 
arrangement  of  the  peripheral  nerve-fibers  of  these  systems  is 
indicated  on  the  right  side.  Figure  70  illustrates  a  cross-sec- 
tion through  the  corresponding  region  of  the  medulla  oblongata 
in  an  early  human  embryo,  whore  the  same  general  arrange- 
ment of  the  sensori-motor  centers  is  evident. 

Figure  71  gives  a  view  of  the  adult  human  medulla  oblongata 
and  midbrain  after  the  removal  of  the  cerebellum  and  mem- 


166 


INTRODUCTION    TO    NEUROLOGY 
A 


Lobus  linese  lateralis 


Fig.  68. — The  medulla  oblouguta  and  cerebellum  of  the  lake  sturgeon 
(Acipenser  rubicundus)  to  show  the  longitudinal  columns  which  have  been 
differentiated  in  correlation  with  the  peripheral  functional  systems.  Com- 
pare Figs.  43  and  44  and  note  that  the  "Lobus  linese  lateralis"  and  "Tuber- 
culum  acustioum"  of  this  figure  together  correspond  to  the  "acoustico- 
lateral  area"  of  the  dogfish.  A  is  a  dorsal  view  with  the  membranous  roof 
of  the  fourth  ventricle  removed  to  show  the  longitudinal  columns  within 
the  ventricle.  B,  C,  and  D  are  sketches  of  cross-sections  at  the  levels 
indicated  in  which  the  four  functional  columns  are  diagrammatically  shaded, 
the  somatic  motor  by  white  circles,  the  visceral  motor  by  white  rectangles, 
the  visceral  sensory  by  oblique  cross-hatching,  and  the  somatic  sensory  by 
vertical  cross-hatching.  The  Roman  numerals  refer  to  the  cranial  nerves. 
(From  Johnston's  Nervous  System  of  Vertebrates.) 


THE    MEDULLA    OBLONGATA    AND    CEREBELLUM 


167 


branous  roof  of  the  fourth  ventricle.     (For  the  form  of  the  ob- 
longata, as  seen  from  the  side  and  from  below,  see  Figs.  45  and 


Somatic  sensory  column 
Visceral  sensory  column 

Visceral  motor  column 
Somatic  motor  column 


Acoustic  area 
Spinal  V  tract 
Vagal  lobe 

Nucleus  ambiguus 
Cutaneous  root  X 
Visceral  sensorj'  root  X 
Visceral  motor  root  X 
Reticular  formation 
Ventral  column 

Spinal  nerve  (XII) 


Fig.  69. — Diagrammatic  cross-section  through  the  medulla  oblongata 
at  the  level  of  the  vagus  nerve  in  a  bony  fish  (the  sea-robin,  Prionotus  caro- 
linus),  to  illustrate  the  arrangement  of  the  four  principal  functional  columns. 

53.)  In  this  figure  the  positions  of  the  primary  sensorj^  and 
motor  nuclei  are  drawn  as  projected  upon  the  dorsal  surface, 
the  motor  centers  on  the  left  and  the  sensory  centers  on  the 


Roof  plate 
Fourth  ventricle 

Dorso-lateral  plate 

Limiting  sulcus 
Ventro-lateral  plate 
X  nerve 
XII  nerve 
Floor  plate 


Somatic  sensory  column 

Visceral  sensory  column 

Visceral  motor  column 
Somatic  motor  column 


Fig.  70. — Diagrammatic  cross-section  through  the  medulla  oblongata 
at  the  level  of  the  vagus  nerve  of  a  human  embryo  of  10.2  mm.  (fifth  week), 
to  illustrate  the  arrangement  of  the  four  principal  functional  columns. 
(Compare  Fig.  69.) 

right.     The  somatic  motor  nuclei  are  indicated  by  circles,  the 
general  visceral  motor  nuclei  by  small  dots,  the  special  vis- 


168 


INTRODUCTION   TO    NEUROLOGY 


Fig.  71. — Dorsal  view  of  the  human  midbrain  and  medulla  oblongata 
after  the  removal  of  the  cerebellum  and  the  roof  of  the  fourth  ventricle, 
with  the  positions  of  the  cranial  nerve  nuclei  projected  upon  the  surface. 
The  motor  nuclei  are  indicated  on  the  left  side  and  the  sensory  nuclei  on  the 
right.  The  somatic  motor  nuclei  are  indicated  by  circles,  the  general  vis- 
ceral efferent  nuclei  by  small  dots,  and  the  special  visceral  efferent  nuclei  by 
large  dots.  The  general  somatic  sensory  area  is  indicated  by  horizontal  lines, 
the  visceral  sensory  area  by  double  cross-hatching,  and  the  special  somatic 
sensory  area  by  open  stipple.     (Compare  Figs.  77,  86,  and  114.) 

n.IV,  nervus  trochlearis;  nuc.com. Cajal,  the  commissural  nucleus  of 
Ramon  y  Cajal;  nuc.III  E-W.,  the  small-celled  visceral  motor  nucleus  of  the 
III  nerve,  or  nucleus  of  Edinger-Westphal;  nuc.III.  lat.,  lateral  nucleus  of 
III  nerve;  nuc.  Ill  yned.,  medial  nucleus  of  III  nerve;  nuc.IV,  nucleus  of  IV 
nerve;  nucmesencV ,  mesencephalic  nucleus  of  V  nerve;  nuc.mot.V,  motor 
nucleus  of  V  nerve;  nuc.mot.V II,  chief  motor  nucleus  of  VII  nerve;  mtc.sal. 
inf.,  nucleus  salivatorius  inferior;  nuc. sal. sup.,  nucleus  salivatorius  superior; 
nuc. sensor. V,  chief  sensory  nucleus  of  V  nerve;  mic.VI,  nucleus  of  VI  nerve; 
nuc.  XII,  nucleus  of  XII  nerve;  n.V,  nervus  trigeminus. 


THE    MEDULLA    OBLONGATA    AND    CEREBELLUM 


169 


ceral  motor  nuclei  by  large  clots,  the  visceral  sensory  nuclei 
by  double  cross-hatching,  the  general  somatic  sensory  nuclei 
by  single  cross-hatching,  and  the  cochlear  and  vestibular 
nuclei  (special  somatic  sensory)  by  open  stipple  bounded  by 
heavy  lines. 

A  more  accurate  mapping  of  the  exact  topographic  relations  between 
the  superficial  landmarks  and  the  underlying  deep  structures  has  re- 
cently been  published  by  Weed  (Publications  of  the  Carnegie -Institution 
of  Washington,  No.  191,  1914),  following  an  earlier  and  less  complete 
study  by  Streeter.     Miss  Sabin  has  published  detailed  reconstructions 


Vagoglossopharyngeal 

roots    Nucleus  of  the 
Restiform    |    fasciculus  solitariua 
body        I  I  Taenia 


Vagus  nucleus 

Fasciculus  solitarius 

Descending  root  of  vestibu- 
lar nerve  (VIII) 
Vago-glossophar- 
yngeal  roots 


Fasc.  long, 
medialis 
Nuc.  spinal  V. 
tract 
Spinal  V.  tr. 
N.  ambiguus 
Olivo-eereb.  tract 
Dorsal  acces.  olive 


External  arcuate  fibers 
Medial  lemniscus 

Medial  acces.  olive 


Inferior  olive 


Pyramid 
Arcuate  nucleus 


Fig.  72. — Cross-section  through  the  adult  human  medulla'  oblongata  at  the 
level  of  the  IX   cranial   nerve.      (From   Cunningham's  Anatomy.) 

(An  Atlas  of  the  Medulla  and  Midbrain,  Baltimore,  1901)  and  a  series  of 
enlarged  models  of  the  internal  anatomy  of  the  brain  stem  of  the  new- 
born babe. 

Figure  72  illustrates  the  appearance  of  a  cross-section 
through  the  adult  human  medulla  oblongata  at  the  level  of  the 
roots  of  the  IX  nerve,  and  Fig.  73  presents  an  analysis  of  a 
section  slightly  nearer  the  spinal  cord  at  the  level  of  the  X 
nerve.  Figure  74  is  a  diagrammatic  representation  of  the 
relations  of  the  four  principal  functional  systems  at  the  same 


170 


INTRODUCTION    TO    NEUROLOGY 


level  as  shown  by  Fig.  73  for  comparison  with  Figs.  66,  67, 
69,  70.  It  is  obvious  that,  while  the  general  relations  in  the 
human  embryo  (Fig.  70)  resemble  tolerably  closely  those  of  the 


Nuc.  dorsalis  vagi 

Nuc.  fasc.  solitarius. 

Fasc.  solitarius 

Nuc.  fasciculus 

J  cuneatus' 

Nuc.  XII 

Spinal  V  nuc. 

Spinal  V  tr.. 

Nuc.  sal.  inf. 

X  root 

Nuc.  ambiguus 


Reticular 
formation 


Inferior  olive 
XII  root 


Ala  cinerea 
Trigonum  hypoglossi 
Nuc.  vestibularis  spinalis 

Fasc.  long.  med. 

Lemniscus  V 


Corpus  resti- 
forme 


Tr.  spino-cereb. 
dorsalis 

Tr.  rubrospinalis 


-  Tr.  spino-cereb. 

ventralis 
Lemniscus 
spinalis 
Tr.  teetospinalis 
■  Lemniscus 
medialis 
Pyramidal  tract 

Fig.  73. — Diagrammatic  cross-section  through  the  human  medulla 
oblongata  at  the  level  of  the  vagus  nerve,  illustrating  details  of  functional 
localization  in  addition  to  those  shown  in  Fig.  72. 


Vise.  mot.  col, 
Som.  mot.  col 


Area  acustica 
Nuc.  fasc.  sol. 
Nuc.  dors.  X 
Fasc.  solitarius 
Cor.  restiforme 
Spinal  V  tract 

Cutan.  root  X 
Vise.  sens,  root  X 
Vise.  mot.  root  X 
Nuc.  ambiguus 
Reticular  form. 
Inferior  olive 
XII  root 


Fig.  74. — Diagrammatic  cross-section  through  the  adult  human  medulla 
oblongata  at  the  same  level  as  shown  in  Fig.  73,  for  comparison  of  the  arrange- 
ment of  the  principal  functional  columns  with  that  of  Figs.  69  and  70. 


adult  fish  (Fig.  69),  in  a  human  adult  (Fig.  74)  this  primary 
arrangement  has  been  greatly  disturbed  by  the  addition  of 


THE    MEDULLA    OBLONGATA    AND    CEREBELLUM  171 

many  new  tracts  and  centers  in  the  ventral  part  of  the 
cross-section. 

We  cannot  here  undertake  an  analysis  of  the  complex  reflex 
connections  of  the  medulla  oblongata.  In  general,  each  of  the 
primary  terminal  nuclei  of  the  sensory  roots  of  the  cranial 
nerves  effects  four  types  of  connections:  (1)  direct  reflex 
connections  with  the  motor  nuclei  of  the  medulla  oblongata, 
these  connections  being  effected  through  the  reticular  forma- 
tion (Figs.  69,  73) ;  (2)  descending  reflex  connections  with  the 
motor  centers  of  the  spinal  cord,  by  way  of  the  bulbo-spinal 
tracts  (such  as  the  vestibulo-spinal  tract,  Fig.  59) ;  (3)  connec- 
tions with  the  cerebellum  (this  applies  only  to  such  functional 
systems  as  have  proprioceptive  value,  of  which  the  vestibular 
nerve  from  the  semicircular  canals  of  the  ear  is  the  most 
important) ;  (4)  connections  with  the  thalamus  and  (after 
a  synapse  here)  with  the  cerebral  cortex. 

The  fibers  of  the  last  type  mentioned  comprise  the  bulbar 
lemniscus  systems.  A  lemniscus  may  be  defined  as  a  central 
system  of  sensory  fibers  terminating  in  the  thalamus.  Its 
fibers  are  axons  of  neurons  of  the  second  order  in  the  pathway 
between  the  peripheral  sense  organs  and  the  cerebral  cortex. 
The  spinal  leniniscus  systems  have  already  been  described 
(p.  150).  Of  the  bulbar  lemniscus  systems  there  are  three 
which  require  special  mention,  viz.,  the  trigeminal  lemniscus, 
the  lateral  lemniscus  and  the  medial  lemniscus.  The  skin  of 
the  face  is  innervated  chiefly  by  the  trigeminal  nerve  (V  pair) 
and  the  fibers  of  this  type  terminate  in  the  general  somatic 
sensory  area  (known  as  the  chief  sensory  V  nucleus  and  the 
spinal  V  nucleus  or  gelatinous  substance  of  Rolando,  Figs. 
71-74).  After  a  synapse  in  this  area  the  fibers  of  the  tri- 
geminal lemniscus  cross  to  the  opposite  side  and  ascend  to  the 
thalamus  in  a  pathway  distinct  from  all  other  lemniscus  fibers 
(see  p.  198  and  Figs.  64,  75,  77,  78,  81). 

The  fibers  of  the  lateral  or  acoustic  lemniscus  arise  from  the 
terminal  nuclei  of  the  cochlear  nerve  (VIII  pair.  Fig.  71),  cross 
at  once  to  the  opposite  side  of  the  brain,  and  ascend  to  the 
midbrain  (Fig.  75) .  Some  of  these  fibers  continue  directly  to 
the  thalamus,  where  they  end  in  the  medial  geniculate  body 
(Fig.  77) ;  others  terminate  in  the  roof  of  the  inferior  coUiculus 


172  INTRODUCTION  TO  NEUROLOGY 

of  the  midbrain.  After  a  synapse  here  and  various  reflex 
connections,  the  nervous  impulse  may  be  carried  forward  to 
the  medial  geniculate  body  of  the  thalamus  by  way  of  the 
brachium  quadrigeminum  inferius  (Figs,  75,  86).  (Regarding 
this  system  see  further  on  pp.  217-227.) 

The  medial  lemniscus  or  fillet  carries  proprioceptive  im- 
pulses from  the  spinal  cord  to  the  thalamus  (pp.  149,  193  and 
Figs.  64,  72  to  75,  77,  78,  83).  Its  fibers  arise  from  the  nucleus 
of  the  fasciculus  gracilis  and  cuneatus  at  the  extreme  lower  end 
of  the  medulla  oblongata,  cross  at  once  to  the  opposite  side 
under  the  ventricle  (decussation  of  the  lemniscus),  and  then 
ascend  directly  to  the  thalamus. 

In  fishes  there  is  an  ascending  secondary  visceral  and  gusta- 
tory tract,  or  visceral  lemniscus,  from  the  visceral  sensory  area 
to  the  midbrain  (p.  273  and  Herrick,  1905) ;  this  tract  no  doubt 
occurs  in  the  human  brain  also,  though  its  exact  course  has 
never  been  demonstrated. 

Having  now  reviewed  cursorily  the  primary  sensory  and 
motor  centers  of  the  medulla  oblongata,  we  must  next  examine 
some  of  the  centers  of  correlation.  As  has  already  been  indi- 
cated, all  of  these  centers  are  interconnected  by  correlation 
neurons  similar  to  those  of  the  spinal  cord  (Figs.  60,  61). 
These  neurons  are  loosely  arranged  in  the  spaces  between  the 
sensory  and  motor  groups  of  nuclei,  this  tissue  being  termed 
the  reticular  formation  (this  region  is  also  called  the  tegmentum, 
see  pp.  69,  138  and  Figs.  69,  74).  But  the  chief  centers  of  cor- 
relation of  the  brain  stem  are  found  in  specially  enlarged  nuclei 
of  the  midbrain  and  thalamus,  some  of  which  are  mentioned  in 
the  next  chapter. 

In  its  more  ventral  parts  the  medulla  oblongata  contains  a 
number  of  large  correlation  centers  and  important  conduction 
pathways  between  remote  parts  of  the  brain.  Of  the  former, 
the  largest  are  the  inferior  ohves  (Figs.  72,  73,  74),  deeply 
buried  masses  of  gray  matter  arranged  in  the  form  of  a  hollow 
shell  of  complex  shape  on  each  side  of  the  median  plane.  The 
olives  receive  fibers  from  the  thalamus  and  spinal  cord  and 
discharge  into  the  cerebellum  (oHvo-cerebellar  fibers  of  Fig. 
72).     Their  functions  are  unknown. 

The  cerebellum  has  already  been  referred  to  as  a  great  supra- 


THE  MEDULLA  OBLONGATA  AND  CEREBELLUM      173 

segmental  mechanism  of  unconscious  motor  coordination.  It 
is  connected  with  the  underlying  brain  stem  by  three  pairs  of 
stalks  or  peduncles,  two  of  which  join  the  medulla  oblongata 
and  one  the  midbrain.  The  inferior  peduncle  (restiform  body) 
connects  with  the  dorsal  margin  of  the  medulla  oblongata  and 
carries  fibers  into  the  cerebellum  from  the  spinal  cord  and  ob- 
longata. The  middle  peduncle  (brachium  pontis)  connects 
with  the  pons  and  most  of  its  fibers  convey  impulses  from  the 
nuclei  of  the  pons  to  the  cerebellum.  The  superior  peduncle 
(brachium  conjunctivum)  connects  with  the  tegmental  region 
of  the  cerebral  peduncle  in  the  floor  of  the  midbrain  and  con- 
tains chiefly  fibers  which  descend  from  the  cerebellum,  cross 
the  midplane  under  the  aqueduct  of  Sylvius,  and  terminate 
in  or  near  the  red  nucleus  (Fig.  75,  nucleus  ruber).  The  inter- 
nal structure  and  connections  of  the  cerebellum  will  be  further 
considered  on  page  204. 

Summary. — The  rhombencephalon  includes  the  medulla 
oblongata  and  cerebellum,  that  is,  all  parts  of  the  brain  below 
the  isthmus.  All  of  the  cranial  nerves  except  the  first  four 
pairs  connect  with  the  medulla  oblongata.  An  analysis  of  the 
functional  components  of  the  cranial  nerves  shows  that  they 
can  best  be  understood  by  considering  each  functional  system 
of  fibers  as  a  unit  and  studying  the  connections  of  each  com- 
ponent separately.  These  connections  are  summarized  in  a 
table  on  pp.  160,  161.  The  medulla  oblongata  of  lower  ver- 
tebrates and  of  the  human  embryo  is  seen  to  be  composed 
chiefly  of  the  primary  centers  related  to  these  functional  com- 
ponents of  the  peripheral  nerves,  arranged  in  longitudinal 
columns  in  the  order  from  dorsal  to  ventral  surfaces  on  each 
side  of  somatic  sensory,  visceral  sensory,  visceral  motor,  so- 
matic motor  centers.  The  same  arrangement  appears  in  the 
adult  human  oblongata,  though  somewhat  distorted  by  the 
presence  of  large  masses  of  correlation  tissue  and  of  large  con- 
duction tracts  which  are  not  present  in  the  lower  vertebrates. 
The  sensory  centers  of  the  oblongata  are  connected  locally 
with  the  adjacent  motor  centers  and  also  by  longer  tracts 
with  the  spinal  cord,  cerebellum,  and  thalamus.  The  latter 
fibers  constitute  the  bulbar  lemniscus,  of  which  several 
functional  components  can  be  distinguished,  the  most  impor- 


174  INTRODUCTION   TO    NEUROLOGY 

tant  being  the  trigeminal  lemniscus  for  general  cutaneous  sen- 
sibility, the  lateral  or  acoustic  lemniscus  for  auditory  sensi- 
bility and  the  medial  lemniscus  for  spinal  proprioceptive 
sensibility.  The  cerebellum  is  a  proprioceptive  center  de- 
veloped out  of  the  vestibular  area  of  the  medulla  oblongata. 

Literature 

The  details  of  the  structure  and  functions  of  the  parts  mentioned  in 
this  and  the  following  chapters  will  be  found  fully  presented  in  the 
standard  text-books  of  human  anatom  y  and  physiology  and  in  the  medical 
text-books  of  neurology,  and  all  of  this  literature  up  to  the  year  1899  is 
summarized  in  Barker's  Nervous  System  and  Its  Constituent  Neurones. 
See  also  W.  von  Bechterew,  Die  Funktionen  der  Nervencentra,  Jena, 
1908  to  1911,  3  vols,  and  Sheldon's  Nervous  System  (New  York,  in 
press).  For  discussions  of  comparative  neurology  and  the  evolution  of 
the  nervous  system,  reference  may  be  made  to  articles  in  the  neurological 
journals,  especially  the  Journal  of  Comparative  Neurology;  see  also  the 
Bibliographies  on  pp.  38,  134,  187,  215,  and  248,  and  the  following  works: 

Bell,  C.     1811.     Idea  of  a  New  Anatomy  of  the  Brain,  London. 

— .  1844.  The  Nervous  System  of  the  Human  Body,  3d.  Ed., 
London. 

— .  1885.  The  Hand,  Its  Mechanism  and  Vital  Endowments,  8th. 
Ed.,  London  (the  Introduction). 

Gaskell,  W.  H.  1886.  On  the  Structure,  Distribution  and  Function 
of  the  Nerves  which  Innervate  the  Visceral  and  Vascular  Systems, 
Jour,  of  Physiol.,  vol.  vii,  pp.  1-80. 

— .  1889.  On  the  Relations  between  the  Structure,  Function,  Dis- 
tribution and  Origin  of  the  Cranial  Nerves,  together  with  a  Theory  of 
the  Origin  of  the  Nervous  System  of  Vertebrata,  Jour,  of  Physiol., 
vol.  X,  pp.  153-211. 

Herrick,  C.  Judson.  1899.  The  Cranial  and  First  Spinal  Nerves  of 
Menidia:  A  Contribution  Upon  the  Nerve  Components  of  the  Bony 
Fishes,  Jour.  Comp.  Neurology,  vol.  ix,  pp.  153-455. 

— .  1905.  The  Central  Gustatory  Paths  in  the  Brains  of  Bony 
Fishes,  Jour.  Comp.  Neur.,  vol.  xv,  pp.  375-456. 

— .  1913.  Brain  Anatomy,  Wood's  Reference  Handbook  of  the 
Medical  Sciences,  3d  ed.,  vol.  ii,  pp.  274-342. 

— .     1914.     Cranial  Nerves,  ibid.,  vol.  iii,  pp.  321-339. 

— .  1914a.  The  Medulla  Oblongata  of  Larval  Amblystoma,  Jour. 
Comp.  Neur.,  vol.  xxiv,  pp.  343-427. 

Johnston,  J.  B.  1906.  The  Nervous  System  of  Vertebrates,  Phila- 
delphia. 

— .     1901.     The  Brain  of  Acipenser,  Zool.  Jahrb.,  Bd.  xv,  pp.  1-204. 

— .  1909.  The  Central  Nervous  System  of  Vertebrates,  Spengel's 
Ergebnisse  und  Fortschritte  der  Zoologie,  Bd.  2,  Heft  2,  Jena. 

Edinger,  L.  1908.  Vorlesungen  iiber  den  Bau  der  nervosen  Zentral- 
organe,  7tli  Auflage,  Band  2,  Vergleichende  Anatomic  des  Gehirns, 
Leipzig. 

— .     1911.     Idem,  8th  Auflage,  Band  1. 


CHAPTER  X 
THE  CEREBRUM 

The  cerebrum  includes  all  of  the  brain  lying  in  front  of  the 
isthmus,  that  is,  the  midbrain  (mesencephalon),  betweenbrain 
(diencephalon),  and  cerebral  hemispheres  (telencephalon),  the 
two  last  comprising  the  forebrain  (prosencephalon).  It  con- 
tains the  primary  sensory  centers  of  the  olfactory  nerves  (I 
pair),  the  sensory  correlation  centers  of  smell  and  sight,  the 
primary  motor  and  sensory  centers  of  the  oculomotor  and 
trochlear  nerves  (III  and  IV  pairs)  for  movements  of  the  eyes, 
and  all  of  the  most  important  higher  correlation  centers  of  the 
brain.  These  higher  correlation  centers  make  up  by  far  the 
larger  part  of  its  substance  in  the  human  brain,  though  in 
fishes  the  converse  relation  prevails,  with  the  primary  sensori- 
motor centers  and  the  simpler  correlation  mechanisms  making 
up  the  larger  part  (see  Figs.  43,  44,  pp.  119,  120). 

The  mesencephalon  (midbrain)  is  that  part  of  the  brain  in 
which  the  early  embryonic  neural  tube  (Figs.  46-51,  pp.  125- 
128)  has  been  least  modified  in  the  adult.  The  ventral  part 
of  the  midbrain,  i.  e.,  the  part  lying  ventrally  of  the  ventricle, 
which  is  here  termed  the  aqueduct  of  Sylvius,  is  called  the  cere- 
bral peduncle ;  the  dorsal  part  is  the  corpora  quadrigemina,  the 
upper  pair  of  these  four  eminences  being  the  superior  colliculi, 
and  the  lower  pair  the  inferior  colliculi  (see  Fig.  71,  p.  168). 

The  corpora  quadrigemina  contain  important  correlation 
centers,  the  superior  colliculus  chiefly  visual  (p.  232)  and  the 
inferior  colliculus  chiefly  auditory  (p.  225).  The  cerebral 
peduncle,  as  the  name  implies,  contains  the  great  ascending  and 
descending  fiber  tracts  between  the  forebrain  above  and  the 
medulla  oblongata,  cerebellum,  and  spinal  cord  below.  The 
arrangement  of  some  of  these  tracts  can  be  seen  in  Fig.  75. 
The  cerebral  peduncle  also  contains  the  nuclei  of  origin  for  the 
motor  fibers  of  the  III  and  IV  pairs  of  cranial  nerves  and  sev- 

175 


176 


INTRODUCTION    TO    NEUROLOGY 


eral  masses  of  gray  matter  devoted  to  motor  coordination, 
such  as  the  black  substance  (substantia  nigra)  and  the  red 
Qucleus  (nucleus  ruber,  see  p.  206). 

The  diencephalon  (betweenbrain  or  thalamencephalon)  in 
early  embryonic  development  is  a  transverse  region  of  the  sim- 
ple neural  tube  (Fig.  48,  p.  126)  surrounding  the  third  ventricle. 

Tectum  mesencephali 
Commissura  tecti 
Nac.  and  tr.  mesen.  V 

Tractus  opticus- y^    ///f[       f^         '^^^>^<^ ^'^'''  'P^°"*'"=*''''' 

_  Brachium  quad-         ///  H.        %^  ^  \Sr%^^^Trigeminal  lenmiscua 

—  ^  \      w    Lateral  and  spinal 


Tr.  cortico- 
bulb.  med 

Fig.  75. — Diagrammatic  cross-section  through  the  midbrain  at  the  level 
of  the  superior  colliculus  (cf.  Fig.  71),  to  illustrate  the  arrangement  of  the 
chief  conduction  pathways:  aq.,  aqueduct  of  Sylvius;  m,  medial  part  of 
motor  nucleus  of  oculomotor  nerve;  n.III,  oculomotor  nerve;  nuc.III, 
motor  nucleus  of  oculomotor  nerve;  Tr.mam.-pedunc,  tractus  mamillo- 
peduncularis.  The  fibers  of  the  dorsal  tegmental  decussation  (Dors.  tegm. 
decuss.,  also  known  as  the  fountain  decussation  of  Meynert)  arise  from 
the  roof  of  the  midbrain  (tectum  opticum)  and  imme'diately  after  crossing 
the  median  plane  descend  toward  the  spinal  cord,  where  they  form  part  of 
the  tractus  tecto-spinalis  (Fig.  59,  p.  141  and  Fig.  73,  p.  170).  The  fibers 
of  the  ventral  tegmental  decussation  {Vent. tegm. demss.,  also  known  as  Forel's 
decussation)  in  a  similar  way  arise  from  the  nucleus  ruber  and  enter  the 
opposite  tractus  rubro-spinalis. 

In  the  adult  human  brain,  however,  it  is  entirely  concealed  by 
other  parts.  The  posterior  part  of  it  is  visible  from  the  side  in 
the  dissection  shown  in  Fig.  45  (p.  123),  its  medial  surface  in 
Fig.  51  (p.  128),  and  its  dorsal  surface  is  exposed  in  the  dissec- 
tion, Fig.  76  (see  also  Fig.  77).     This  part  of  the  brain  is 


THE    CEREBRUM 


177 


devoted  wholly  to  various  types  of  correlation.  It  has  three 
main  cUvisions,  the  thalamus,  the  epithalanuis,  and  the  hypo- 
thalamus, of  which  the  last  two  are  dominated  by  the  olfactory 
apparatus  (see  p.  245). 

The  epithalamus  consists  of  the  membranous  roof  of  the  third 
ventricle  (Fig.  79),  including  the  choroid  plexus  of  the  third 
ventricle    (p.  133),   the   pineal   body   or  epiphysis  (Fig.  76), 


*'*^^?JV\| 


Non-ventricular  part  of- 
thalamus 

Groove  correspondin: 

to  fornix 
Quadrigeminal  bodies- 

Trochlear  nerve- 

Brachimn  pontis- 

Brachium  conjunctivum 

Lingula 


Medulla  oblongata 


Genu  of  corpus  callosmn 
Corpus  callosum  (cut) 

Cavum  eepti  pellucidi 
Septum  pellucid  um 

-Caudate  nucleus 

Fornix 

Foramen  interventriculare 
Anterior  conunissure 
Ant.  tubercle  of  thalamus 
Massa  intermedia 

Third  ventricle 
Stria  terminalis 
Taenia  thalami 
Trigonum  habenuls 
Posterior  commissure 
Stalk  of  pineal  body 
Pulvinar 
ineal  body 


Fig.  76. — A  dissection  of  the  brain  from  above  to  expose  the  thalamus  and 
corpus    striatum.      (From    Cunningham's    Anatomy.) 

the  habenula  (marked  trigonum  habenulsB  on  Fig.  7G),  and 
the  stria  medullaris,  a  fiber  tract  which  connects  the  olfac- 
tory centers  of  the  cerebral  hemispheres  with  the  habenula 
(Figs.  78,  79).  The  habenula  is  a  center  for  the  correlation 
of  olfactory  sensory  impulses  with  the  various  somatic  sen- 
sory centers  of  the  dorsal  part  of  the  thalamus.  The  pineal 
body  of  some  lower  vertebrates  is  a  sense  organ,  apparently 
visual  in  function  and  known  as  the  parietal  eye  (p.  237);  in 

12 


178 


INTRODUCTION   TO    NEUROLOGY 

Tornix 


Lemnis.  spinalis- 

Lemnis.  medialia- 

Lenmis.  lateralis" 

Lemniscus  V- 


Superior  olive -| 


^ 


Nuclei  of  funiculi  gracilis 
and  cuneatus 


n          '        1 

Mesencephalic 

^'     ^ 

\  -t 

nucleus  V 
n.  V  motor 

^^— 

^ 

n.  V  sensory 

Chief   sensory 

nucleus  V 

R  \                       /  Nue.  vestib.  VIII 
H^— \^               /   n-VII 

J^         X      " 

VIII 

IX 

X 

_Nuc.  cochlearis  VIII 

Fasciculus  solitarius 

Nuc.  commissurahs  of  Cajal 


Nucleus  spinalis  V 


Fig.  77. — A  diagram  of  the  human  brain  stem  from  above  after  the  re- 
moval of  the  cerebral  hemispheres,  to  illustrate  the  nuclei  of  the  thalamus 
and  some  of  the  chief  fiber  tracts  connected  with  them.  Compare  Figs.  71 
and  45.  The  fibers  of  the  sensory  radiations  between  the  thalamus  and  the 
cerebral  cortex  fall  into  three  groups:  somesthetic  (som.)  for  touch,  tempera- 
ture, and  spatial  discrimination,  auditory  Caw.),  and  optic  (opt.).  Descend- 
ing cortico-thalamic  fibers  are  shown  in  connection  with  the  somesthetic 
radiation  only;  but  such  fibers  are  present  in  the  auditory  and  optic  radia- 
tions also,     ant.,  anterior  nucleus  of  thalamus;  ep.,  pineal  body  (epiphysis); 


THE    CEREBRUM  179 

man  its  primary  sensory  function  is  lost  and  it  is  said  to 
produce  an  important  internal  secretion  whose  physiological 
value  is  still  obscure. 

The  hypothalamus  includes  the  tuber  cinereum  and  mammil- 
lary  bodies  (see  Figs.  53,  78,  and  79),  these  structures  being 
olfactory  centers,  and  the  hypophysis  or  pituitary  body  (which 
has  been  removed  from  the  specimen  shown  in  Fig.  53,  its  point 
of  attachment  being  the  infundibulum) .  The  hypophysis  is  a 
glandular  organ  which  produces  an  internal  secretion  of  great 
importance  in  maintaining  the  proper  balance  of  the  metabolic 
activities  of  the  body.  The  hypothalamus  is  an  important 
center  for  the  correlation  of  olfactory  impulses  with  various 
visceral  functions,  including  probably  the  sense  of  taste. 

The  thalamus  is  in  the  human  brain  chiefly  a  sort  of  vestibule 
through  which  the  systems  of  somatic  sensory  nervous  impulses 
reach  the  cerebral  cortex.  There  are,  however,  two  parts  of 
the  thalamus  which  should  be  clearly  distinguished.  The 
ventral  part  contains  chiefly  motor  coordination  centers.  It  is 
feebly  developed  in  the  human  brain,  where  it  is  termed  the 
subthalamus  (not  to  be  confused,  as  is  often  done,  with  the 
hypothalamus,  see  Figs.  78,  79,  and  81).  The  dorsal  part  of 
the  thalamus,  in  its  turn,  contains  two  distinct  types  of  sensory 
correlation  centers:  (1)  primitive  sensory  reflex  centers,  chiefly 
in  the  medial  group  of  thalamic  nuclei;  (2)  the  more  lateral 
nuclei  which  form  the  cortical  vestibule  to  which  reference  was 
made  above.  These  lateral  nuclei  are  sometimes  called  the 
new  thalamus  (neothalamus)  in  distinction  from  all  of  the  other 
thalamic  nuclei  which  form  the  old  thalamus  (palseothalamus) . 

The  centers  which  comprise  the  new  thalamus  make  up  by 
far  the  larger  part  of  the  thalamus  in  the  human  brain  and 
include  the  following  nuclei:  the  lateral,  ventral,  and  posterior 
nuclei  (for  general  cutaneous  and  deep  sensibility)  receiving 
the  spinal,  trigeminal,  and  medial  lemnisci;  the  lateral  genicu- 

c.g.l.,  corpus  geniculatum  laterale;  c.g.m.,  corpus  geniculatum  mcdiale;  col. 
inf.,  colliculus  inferior;  col.  sup.,  collieulus  superior;  lat.,  lateral  nucleus 
of  thalamus;  mcd.,  medial  nucleus  of  thalamus;  post.,  posterior  nucleus  of 
thalamus;  pulv.,  pulvinar;  vcnlr.,  ventral  nucleus  of  thalamus.  Root  fibers 
of  the  X  nerve,  in  addition  to  those  of  the  VII  and  IX  nerves,  should  be  shown 
entering  the  fasciculus  solitarius  (cf.  Fig.  114).  Those  of  the  VII  and  IX 
nerves  are  chiefly  gustatory. 


180 


INTRODUCTION    TO    NEUROLOGY 


late  body  and  pulvinar  (visual  sensibility)  receiving  the 
optic  tracts;  the  medial  geniculate  body  (auditory  sensibility) 
receiving  the  lateral  or  acoustic  lemniscus.  The  lateral  and 
medial  geniculate  bodies  comprise  the  metathalamus  of  the 
B.  N.  A.  (see  p.  130  and  Fig.  50,  p.  127),  which  in  this  work  are 
described  as  part  of  the  thalamus. 

All  of  the  thalamic  nuclei  of  the  lateral  group  (the  neothala- 
mus) are  connected  by  important  systems  of  fibers  with  the 
cerebral  cortex,  these  fibers  running  both  to  and  from  the  cor- 
tex (Fig.  77).     These  are  called  sensory  projection  fibers  and 


Corpus  callosum,^ 

Fimbria^ 

Nucleus  anterior^ 

Tr.  mamillo-thalamicusv 

Nucleus  lateralis,, 

Metathalamus^ 


Habenula-  -/^ 

Fasc.  ret.- 
Nuc.  post.- 
Nuc.  ven— 
Subthal.-  —"^rr^ 

Nuc.  ruber 

Lemn.  V 

Br.  conj 

S.  nigra 

Lemn.  med. 

Tr.  th.-ped.       


Fig.  78. — Diagram  of  the  nuclei  of  the  diencephalon  and  some  of  their 
functional  connections  as  seen  in  parasagittal  section.  The  epithalamus 
and  the  hypothalamus  are  stippled.  Br. conj.,  brachium  conjunctivum; 
Fasc.ret.,  fasciculus  retroflexus;  Lemn.  med.,  lemniscus  medialis;  Lemn.V., 
lemniscus  trigemini;  Nuc. post.,  nucleus  posterior  thalami;  Nuc.ven.,  nucleus 
ventralis  thalami;  Subthal.,  subthalamus;  S.nigra,  substantia  nigra;  Tr.th.-ped., 
tractus  thalamo-peduncularis.  This  diagram  should  be  studied  in  connection 
with  a  median  section  of  the  entire  brain  such  as  is  shov/n  in  Figs.  51  and 
52,  p.  128. 

all  pass  through  or  near  the  internal  capsule  of  tlie  corpus 
striatum  (p.  184).  As  we  have  just  seen,  the  nuclei  of  the 
lateral  group  receive  special  systems  of  somatic  sensory  fibers — 


THE    CEREBRUM 


181 


optic,  acoustic,  and  the  general  cutaneous  and  deep  sensibility 
complex  of  the  spinal,  trigeminal,  and  medial  lemnisci.  The 
elements  of  the  latter  complex  (comprising  touch,  temperature, 
pain,  general  proprioceptive  sensibility,  spatial  localization, 
etc.,  termed  as  a  whole  the  somesthetic  group)  are  no  doubt 
separately  represented  in  the  thalamus,  but  the  analysis  of 
their  respective  thalam'ic  centers  has  not  yet  been  completely 
effected.     Each  of  the  chief  functional  regions  of  the  neothala- 


Corona  radiata 
Caudate  nucleus 


Lateral  (Sylvian) 

fissure 
Internal  capsule 

Island  of  Reil 
Lentiform  nucleus 

External  capsule 


Corpus  callosum 

Fornix 

Chorioid  plexus 

Stria  medullaris 

Nuc.  ant.  thai. 

Nuc.  medial,  thai. 

Nuc.  lateral,  thai. 

Nuc.  ventral,  thai. 

Subthalamus 

Mammillary  body 

Optic  tract 
Amygdala. 

Lateral  ventricle 

Fig.  79. — Cross-section  through  the  human  cerebral  hemisphere  and 
thalamus,  including  the  mammillary  bodj^  and  the  posterior  end  of  the  an- 
terior nucleus  of  the  thalamus  (cf.  Fig.  78).  At  this  level  the  epi thalamus 
is  represented  only  by  the  stria  medullaris  and  the  chorioid  plexus  of  the 
third  ventricle,  the  hypothalamus  by  the  mammillarj'  body.  The  old 
thalamus  (palseothalamus)  is  represented  by  the  anterior  and  medial  nuclei 
and  the  subthalamus,  the  new  thalamus  (neothalamus)  by  the  lateral  and 
ventral  nuclei. 


mus  which  have  just  been  enumerated  is  connected  b}^  its 
own  system  of  projection  fibers  with  a  specific  region  in  the 
cerebral  cortex,  viz.,  the  optic,  auditory,  and  somesthetic 
projection  centers  (see  p.  318).  These  tracts  are  known  as  the 
optic,  auditory,  and  somesthetic  radiations  (see  Fig.  80). 

The  old  thalamus  (palseothalamus)  comprises  the  more 
medial  thalamic  centers  which  were  differentiated  for  the 
primitive  thalamic  correlations  which  are  present  in  fishes  and 


182  INTRODUCTION  TO  NEUROLOGY 

other  lower  vertebrates  which  lack  the  cerebral  cortex  (see 
Herrick,  1917).  Chnical  evidence  (see  especially  Head  and 
Holmes,  1911)  seems  to  show  that  many  of  these  primitive 
functions  are  retained  in  the  old  thalamus  in  man,  and  that 
some  of  the  conscious  activities  are  served  by  these  thalamic 
centers.  In  other  words,  the  activity  of  the  cerebral  cortex 
is  not  essential  for  all  conscious  processes,  though  its  partici- 
pation is  necessary  for  others,  particularly  all  intellectual  and 
voluntary  activities.  The  thalamus,  on  the  other  hand,  can 
act  independently  of  the  cortex  in  the  case  of  painful  sensibility 
and  the  entire  series  of  pleasurable  and  painful  qualities;  for 
the  thalamic  centers  when  isolated  from  their  cortical  con- 
nections are  found  to  be  concerned  mainly  with  affective  ex- 
perience, and  destructive  lesions  which  involve  the  cortex 
alone  do  not  disturb  the  painful  and  affective  qualities  of 
sensation  (see  p.  281). 

The  experiments  of  Rogers  (1916)  on  decerebrate  birds 
support  the  belief  that  the  thalamus  contains  mechanisms 
for  visceral  adjustment  which  are  lacking  in  the  cerebral  cor- 
tex. He  concludes  that  in  birds  with  the  thalamus  intact 
and  the  cerebral  hemispheres  removed  the  inhibitory  effects 
of  external  stimuli  (especially  light  and  sound)  upon  visceral 
movements  are  lost,  but  that  effects  of  visceral  and  painful 
stimuli  are  preserved.  He  shows,  further,  that  the  well- 
known  restlessness  of  decerebrate  birds  (somatic  movements 
of  walking  about,  etc.)  is  not  primarily  excited  by  external 
(somatic  sensory)  stimuli,  but  by  various  types  of  visceral 
activity. 

The  relations  of  the  thalamic  nuclei  and  of  some  of  the  tracts 
connected  with  them  are  shown  as  seen  from  above  in  Fig.  77 
and  in  a  section  parallel  with  the  median  plane  in  Fig.  78. 
Some  of  these  centers  are  seen  in  cross-section  in  Fig.  79.  The 
preceding  analysis  of  the  diencephalon,  which  differs  in  some 
respects  from  that  of  the  B.  N.  A.  (p.  130),  is  summarized  in 
the  accompanying  table  (p.  183),  which  includes  also  a  few 
of  the  more  important  fiber  tracts  connected  with  each  nucleus. 

In  front  of  the  thalamus  lie  the  corpus  striatum  and  olfactory 
centers  (see  Fig.  45,  p.  123),  and  above  these  last  two  is  spread 
the  great  expanse  of  the  cerebral  cortex  or  pallium.     The  cor- 


THE    CEREBRUM  183 

The  Diencephalon 

I.  Epithalamus. 

1.  Memb'-anous  roof  of  the  third  ventricle. 

2.  Pineal  body  (epiphysis). 

3.  Habenula   (receives  the  stria  medullaris  from  the  olfactory 

centers  and  sends  fibers  to  the  cerebral  peduncle). 
II.  Thalamus. 

1.  Dorsal  part. 

(1)  Medial  group  of  nuclei. 

(a)  Medial  nucleus  (receives  fibers  from  the  olfactory 

area  and  neothalamus  and  from  the  trigeminal 
lemniscus;  sends  fibers  to  the  olfactoiy  area, 
corpus  striatum,  subthalamus,  and  probably 
cerebral  cortex). 

(b)  .\nterior  (or  dorsal)  nucleus  (receives  fibers  from 

the  mammillary  body  and  sends  fibers  to  the 
corpus  striatum). 

(2)  Lateral  group  of  nuclei  (neothalamus). 

(a)  Lateral,  ventral,  and  posterior  nuclei  (receive  che 
medial,  spinal,  and  trigeminallemnisci;  connect 
with  parietal  and  frontal  cortex  by  ascending 
and  descending  somesthetic  projection  fibers). 

(fe)  Pulvinar  and  lateral  geniculate  body  (receive  optic 
tracts;  connect  with  occipital  cortex  by  ascend- 
ing and  descending  optic  projection  fibers). 

(c)  Medial  geniculate  body    (receives  the  lateral  or 

acoustic  lemniscus;  connects  with  temporal  cor- 
tex by  ascending  and  descending  auditory  pro- 
jection fibers). 
[The  two  geniculate  bodies  =metathalamus,  B.  N.  A.] 

2.  Ventral  part,  or  subthalamus  (a  motor  coordination  center 

receiving  fibers  from  the  dorsal  part  of  the  thalamus,  from 
the  corpus  striatum  and  from  the  pyramidal  tract;  sends 
fibers  to  the  pedunculus  cerebri;  comprises  the  body  of 
Luys,  Forel's  field  Ho,  and  some  adjacent  gray  matter;  is 
continuous  behind  with  the  substantia  nigra  of  the  cerebral 
peduncle). 
Ill    Hypothalamus. 

1.  Tuber  cinereum  (olfacto-visccral  correlation  center). 

2.  Mammillarj''  body  (receives  fibers  from  the  olfactory  centers; 

sends  fibers  to  the  cerebral  peduncle  and  nucleus  anterior 
thalami). 

3.  Hypophysis. 

pus  striatum  consists  of  masses  of  gray  matter  separated  by 
sheets  of  white  matter,  an  arrangement  which  gives  a  striated 
appearance  in  section. 

In  stud3'ing  the  comparative  anatomy  of  the  cerebral  hemi- 
spheres we  find  the  corpus  striatum  well  developed  in  some 


184 


INTRODUCTION   TO   NEUROLOGY 


Gyms  frontalis  inf. 
Gyrus  cinguli 
Corpus  callosum 
External  capsule 
Lateral  ventricle 
Caudate  nucleus 


Anterior  limb  of 
internal  capsule 


Column  of  fornix 
Lentiform  nucleus 


Posterior  limb  of 
internal  capsule 


Medial  nucleus  of 
thalamus 
Third  ventricle 

Pulvinar 
Habenula' 
Lateral  ventricli 


Lateral  nucleus  of 

thalamus 
Hippocampal  com. 

Corpus  callosum 

Caudate  nucleus 

Parieto-occip.  fissure 

Cuneus 


Fig.  80. — Longitudinal  section  through  the  human  cerebral  hemisphere 
passing  through  the  internal  capsule,  some  of  the  fiber  systems  of  which  are 
numbered  as  listed  below: 

1.  Frontal  thalamic  tracts  between  the  medial  nucleus  of  the  thalamus 
and  the  frontal  lobe  of  the  cerebral  cortex. 

2.  Frontal  pontile  tract  between  the  frontal  lobe  of  the  cortex  and  the 
pons. 

3.  Cortico-oculomotor  tract  from  the  motor  cortex  to  the  nucleus  of  the 
oculomotor  nerve. 

4.  Cortico-bulbar  tracts  from  the  motor  cortex  to  the  motor  nuclei  of  the 
medulla  oblongata. 


THE    CEREBRUM  185 

lower  vertebrates  which  lack  the  cerebral  cortex,  and  very 
highly  developed  in  others,  like  reptiles  and  birds,  where  the 
cortex  is  present,  though  very  small.  In  these  animals  the 
corpus  striatum  appears  to  be  a  reflex  center  of  great  impor- 
tance and  of  higher  order  than  the  thalamus;  and  the  differ- 
entiation of  this  apparatus  seems  to  have  been  a  necessary 
precursor  of  the  elaboration  of  the  cerebral  cortex  as  we  find 
it  in  the  mammals. 

The  functions  of  the  mammalian  corpus  striatum  are  very 
obscure.  It  is  connected  by  both  ascending  and  descending 
fibers  with  various  nuclei  of  the  thalamus  and  cerebral  peduncle, 
and  also  with  the  cerebral  cortex.  Ramon  y  Cajal  is  of  the 
opinion  that  the  mammalian  striatum  functions  chiefly  to  re- 
inforce the  descending  motor  impulses  which  leave  the  cerebral 
cortex,  these  systems  of  fibers  giving  off  collateral  branches  as 
they  traverse  it,  and  the  striatum  itself  sending  important 
descending  tracts  into  the  thalamus  and  cerebral  peduncle. 

The  white  matter  of  the  corpus  striatum  consists  partly  of 
the  fibers  already  mentioned  as  passing  between  it  and  the 
thalamus  and  cortex,  but  chiefly  of  fibers  passing  between  the 
cortex  and  deeper  parts  of  the  brain  stem,  having  no  functional 
connection  with  the  striatum  itself.  These  are  called  pro- 
jection fibers.  They  are  partly  ascending  and  descending 
fibers  passing  between  the  thalamus  and  the  cortex  (the  optic, 
auditory,  and  somesthetic  projection  systems,  or  radiations. 


6.  Cortico-rubral  tract  from  the  motor  cortex  to  the  nucleus  ruber. 
6  to  10.  Pyramidal  tract  (tractus  cortico-spinaHs)  from  the  motor  cortex 
to  the  spinal  cord,  with  the  following  parts — 

6.  To  the  cervical  spinal  cord  for  the  muscles  of  the  shoulder. 

7.  To  the  cervical  cord  for  the  muscles  of  the  arm. 

8.  To  the  cervical  cord  for  the  muscles  of  the  hand. 

9.  To  the  lumbar  cord  for  the  muscles  of  the  leg. 

10.  To  the  lumbar  cord  for  the  muscles  of  the  foot. 

11.  Somesthetic  radiations  from  the  lateral  and  ventral  nuclei  of  the  thala- 
mus to  the  cerebral  cortex. 

12.  Occipito-temporal  pontile  tract  to  the  pons,  and  temporo-thalamic-  tract 
to  the  thalamus. 

13.  Auditory  radiation   from   the  medial   geniculate  body  to  the  superior 
temporal  gyrus. 

14.  Optic  radiation  from   the   pulviuar  and  lateral  gonicvilate  body  to  the 
cuneus  in  the  occipital  lobe  of  the  cortex. 


186  INTRODUCTION    TO    NEUROLOGY 

which  have  already  been  mentioned,  p.  180),  and  partly 
descending  motor  projection  fibers  of  the  cortico-spinal  or 
pyramidal  tract  (p.  151  and  Fig.  64,  p.  152),  cortico-bulbar 
tract,  and  cortico-pontile  tracts  (pp.  206  and  315). 

The  gray  matter  of  the  corpus  striatum  is  gathered  into  two 
principal  masses,  the  caudate  nucleus  and  the  lentiform  nucleus 
(so-named  from  their  shapes),  and  most  of  the  projection  fibers 
pass  between  these  nuclei  in  a  wide  band  of  white  matter 
known  as  the  internal  capsule.  The  broken  ends  of  the  inter- 
nal capsule  fibers  are  seen  in  the  dissection  shown  in  Fig.  45 
(p.  123).  As  these  fibers  radiate  from  the  internal  capsule 
toward  the  cortex  they  are  called  the  corona  radiata  (Fig.  79) . 
The  external  capsule  is  a  thinner  sheet  of  fibers  externally  of 
the  lentiform  nucleus  (Figs.  79  and  80).  Figure  79  illustrates 
a  transverse  section  through  the  cerebral  hemisphere,  showing 
the  relations  of  the  thalamus  and  corpus  striatum. 

The  exact  arrangement  of  the  functional  systems  of  sensory 
and  motor  projection  fibers  within  the  internal  capsule  is  a 
matter  of  great  clinical  importance;  for  a  considerable  propor- 
tion of  apoplexies  and  other  cerebral  diseases  result  from 
hemorrhage  or  other  injury  of  the  internal  capsule  causing 
destruction  of  some  of  its  fibers.  A  partial  paralysis  will  result, 
whose  symptoms  will  depend  upon  the  particular  functional 
systems  of  projection  fibers  affected.  Figure  80  illustrates  the 
arrangement  of  some  of  the  systems  of  fibers  of  the  internal 
capsule  as  seen  in  a  horizontal  section  through  the  cerebral 
hemispheres. 

The  olfactory  centers  of  the  cerebral  hemispheres  and  the 
cerebral  cortex  will  be  considered  in  chapters  which  follow. 

Summary. — The  cerebrum  contains  the  primary  centers  for 
the  I,  II,  III,  and  IV  pairs  of  cranial  nerves,  but  most  of  its 
substance  is  concerned  with  the  higher  centers  for  the  correla- 
tion of  sensory  impressions,  especially  those  involved  in  the 
psychic  activities.  The  midbrain  contains  in  the  corpora 
quadrigemina  important  reflex  correlation  centers  of  sight  and 
hearing,  and  in  the  cerebral  peduncle  centers  for  the  coordina- 
tion of  movements.  The  diencephalon  is  devoted  chiefly  to 
various  types  of  correlation.  It  is  divided  into  three  parts, 
the  thalamus,  the  epithalamus,  and  the  hypothalamus,  the 


THE    CEREBRUM  187 

two  last  being  dominated  by  the  olfactory  system.  The 
thalamus  contains  a  medial  group  of  nuclei  concerned  with 
thalamic  reflexes  and  the  affective  experience  and  a  lateral 
group  of  nuclei  which  discharge  the  sensory  projection  fibers  of 
sight,  hearing,  and  general  sensibility  into  the  cerebral  cortex. 
The  subdivision  of  the  diencephalon  is  summarized  in  the 
table  on  p.  183.  The  corpus  striatum  in  lower  vertebrates  is 
iin  important  reflex  center;  in  man  its  functions  seem  to  be 
subsidiary  to  those  of  the  cerebral  cortex  for  the  most  part. 
It  consists  of  two  chief  masses  of  gray  matter,  the  caudate  and 
lentiform  nuclei,  with  sheets  of  white  matter  between  and 
within  these  masses.  The  chief  systems  of  fibers  of  the  white 
matter  are  accumulated  in  the  internal  capsule  which  lies 
between  the  lentiform  nucleus  laterally  and  the  caudate 
nucleus  and  thalamus  medially.  Through  the  internal  cap- 
sule run  the  projection  fibers  which  connect  the  cerebral  cor- 
tex with  the  lower  parts  of  the  brain  stem,  including  the  sen- 
sory radiations  from  the  thalamus  and  the  descending  systems 
to  the  pons  and  brain  stem  and  the  great  pyramidal  tract, 
which  is  the  voluntary  motor  path  from  the  cortex  to  the 

spinal  cord. 

Literature 

Crosby,  Elizabeth  C.  1917.  The  Forebrain  of  Alligator  mississip- 
piensis.  Jour.  Comp.  Neur.,  vol.  xxvii,  pp.  325-402. 

Head,  H.,  and  Holmes,  G.  1911.  Sensory  Disturbances  from 
Cerebral  Lesions,  Brain,  vol.  xxxiv,  pp.  109-254. 

Herrick,  C.  Judson.  1910.  The  Morphology  of  the  Forebrain  in 
Amphiiaia  and  Reptilia,  Jour.  Comp.  Neur.,  vol.  xx,  pp.  413-.547. 

— .  1913.  Article  Brain  Anatomy,  in  Wood's  Reference  Handbook 
of  the  Medical  Sciences,  3d  ed.,  vol.  ii,  pp.  274-342. 

— .  1917.  The  Internal  Structure  of  the  Midbrain  and  Thalamus 
of  Necturus,  Jour.  Comp.  Neur.,  vol.  xxviii,  pp.  215-348. 

Johnston,  J.  B.  1906.  The  Nervous  System  of  Vertebrates, 
Philadelphia. 

— .  1909.  The  Morphology  of  the  Forebrain  Vesicle  in  Vertebrates, 
Jour.  Comp.  Neur.,  vol.  xix,  pp.  457-539. 

— .  1913.  The  Morphology  of  the  Septum,  Hippocampus,  and 
Pallial  Commissures  in  Reptiles  and  Mammals,  Jour.  Comp.  Neur., 
vol.  xxiii,  pp.  371-478. 

— .  1915.  The  Cell  Masses  in  the  Forebrain  of  the  Turtle,  Cistudo 
Carolina,  Jour.  Comp.  Neur.,  vol.  xxv,  pp.  393-468. 

— .  1916.  Evidence  of  a  Motor  Pallium  in  the  Forebrain  of  Reptiles, 
Jour.  Comp.  Neur.,  vol.  xxvi,  pp.  475-479. 

V.    MoNAKOW,    C.     1895.     Experimentelle    und  pathologische-anat- 


188  INTRODUCTION  TO  NEUROLOGY 

omische  Untersuchungen  liber  die  Haubenregion,  den  Sehhiigel  und  die 
Regio  subthalamica,  Arch.  f.  Psychiat.,  Bd.  27. 

Rogers,  F.  T.  1916.  Contributions  to  the  Physiology  of  the 
Stomach,  XXXIX.  The  Hunger  Mechanism  of  the  Pigeon  and  its 
Relation  to  the  Central  Nervous  System,  Am.  Jour.  Physiol.,  vol.  xU, 
pp.  555-570. 

Sachs,  E.  1909.  On  the  Structure  and  Functional  Relations,  of  the 
Optic  Thalamus,  Brain,  vol.  xxxii,  pp.  95-186. 

Sheldon,  R.  E.  1912.  The  Olfactory  Tracts  and  Centers  in  Teleosts 
Jour.  Comp.  Neur.,  vol.  xxii,  pp.  177-339. 


CHAPTER  XI 

THE    GENERAL    SOMATIC     SYSTEMS    OF    CONDUCTION 

PATHS 

In  this  and  the  following  chapters  we  shall  review  the  con- 
duction pathways  followed  by  some  of  the  chief  sensori-motor 
systems  and  add  some  further  details  to  the  general  description 
already  given,  beginning  with  the  more  generalized  somatic 
sensory  functions. 

Clinical  neurologists  have  long  been  in  the  habit  of  grouping 
together  the  different  forms  of  deep  and  cutaneous  sensibility 
under  the  term  "general  sensibility."  The  more  refined  re- 
searches of  recent  students  (especially  Sherrington,  Head, 
Trotter  and  Davies,  Brouwer,  Boring,  see  the  bibliographies  on 
pp.  100  and  153)  have  given  us  a  much  more  precise  analysis 
of  these  systems,  as  already  explained.  The  peripheral 
nerves  of  deep  sensibility  (exclusive  of  those  devoted  to 
strictly  visceral  functions)  are  anatomically  distinct  from 
those  of  cutaneous  sensibility.  Physiologically,  the  nerves  of 
deep  sensibility  are  devoted  chiefly  to  proprioceptive  functions 
(muscle  sensibility,  joint  sensibility,  etc.),  and  the  nerves  of 
cutaneous  sensibility  chiefly  to  exteroceptive  functions  (touch, 
temperature,  and  pain) ;  but  this  holds  only  approximately,  for 
nerves  of  deep  sensibility  may  also  serve  the  exteroceptive 
functions  of  pressure  and  painful  response  to  overstimulation, 
though  with  a  higher  stimulus  threshold  than  in  the  skin,  and 
the  cutaneous  nerves  also  participate  to  some  extent  in  the 
proprioceptive  functions  of  spatial  orientation  of  the  body  and 
its  members  (see  pp.  82  ff.  and  143). 

Exteroceptive  Systems. — The  nerves  serving  the  functions 
of  touch,  pressure,  temperature,  and  pain  of  the  body  and 
limbs,  whether  derived  from  the  skin  or  the  deep  tissues,  im- 
mediately after  their  entrance  into  the  spinal  cord  terminate  in 
the  gray  matter  of  the  dorsal  column  of  the  same  side.     After 

1S9 


190 


INTRODUCTION    TO    NEUROLOGY 


fo  cortex 


subthalamus 

trigeminol 
lemniscus 


lateral  lemniscus 
medial  lemniscu 


Ynerve 
Ynudeus 


5pinal  V  Tract 
reticular  formation 


Spinal  Ytracl"- 


spinalVnudeus 


-6.  Touch  and  pressure 
-J.  pain  and  temperature 
=]■  spinal  lemniscus 


Fig.  81. — Diagram  of  the  exteroceptive  conduction  pathways  contained 
within  the  spinal  cord  and  brain  stem.  The  figure  illustrates  cross-sections 
of  the  central  nervous  system  in  the  lower  cervical  region  of  the  spinal 
cord,  at  the  level  where  the  cord  passes  over  into  the  medulla  oblongata,  at 
the  level  of  the  roots  of  the  VIII  cranial  nerve,  through  the  inferior  colliculus 
and  through  the  thalamus. 

1.  Connections  of  peripheral  neuron  of  touch,  temperature,  or  pain  for 
intrinsic  spinal  reflexes. 

3.  Peripheral  neuron  of  pain  or  temperature. 


GENERAL   SOMATIC    SYSTEMS    OF    CONDUCTION    PATHS  101 

a  synapse  here  the  axons  of  the  neurons  of  the  second  order 
cross  to  the  opposite  side  of  the  cord  and  ascend  in  the  spinal 
lemniscus  to  the  thalamus.  For  further  details  of  these  con- 
nections see  pages  149-151,  178-182,  and  Figs.  59,  63,  64,  75, 
77,  78,  80,  81;  on  the  pain  path,  see  also  p.  279.  The  pathway 
for  cutaneous  sensibility  from  the  head  follows  the  trigeminal 
lemniscus  (pp.  171,  197,  and  Figs.  64,  75,  77,  78,  81).  The 
more  important  exteroceptive  pathways  are  assembled  in 
Fig.  81. 

It  will  be  recalled  that  in  the  spinal  lemniscus  the  pathways 
for  touch  and  pressure,  for  pain  and  for  temperature  are  assem- 
bled in  three  distinct  tracts,  those  for  pain  and  temperature 
being  close  together  (Fig.  63,  p.  150).  From  this  it  follows 
that  small  circumscribed  injuries  in  the  white  substance  of  the 
spinal  cord  may  destroy  all  sensibihty  to  pressure  in  a  part  of 
the  body  without  any  considerable  disturbance  of  pain  or  tem- 
perature sensibility,  or  conversely,  it  may  destroy  pain  or 
temperature  sensibility  without  any  involvement  of  the  other 
qualities  of  sensation.  And,  in  fact,  in  numerous  clinical 
cases  these  conditions  are  found,  as  will  be  clear  from  the 
following  example. 

Figure  82  illustrates  such  a  case  from  Dr.  Head's  experience. 
The  patient  suffered  from  an  injury  to  the  lower  part  of  the 
spinal  cord  caused  by  the  overturning  of  a  truck  of  concrete, 
and  when  admitted  to  the  London  Hospital  was  paralyzed  from 
the  hips  downward.  In  the  course  of  a  year  he  partlj^  re- 
covered, but  showed  a  permanent  loss  of  some  sensation 
qualities  over  the  shaded  area  in  the  figure.  The  right  leg 
below  the  knee  was  insensitive  to  pain  (prick)  and  to  all 
degrees  of  temperature.     But  over  the  whole  of  this  area  he 

3.  Peripheral  neuron  of  touch  and  pressure. 

4.  Peripheral  motor  neurons  of  spinal  nerve. 

5.  Peripheral  cutaneous  neuron  of  trigeminal  nerve. 

6.  Secondary  neuron  of  touch  and  pressure  in  spinal  lemniscus. 

7.  Secondary  neuron  of  pain  or  temperature  in  spinal  lemniscus. 

8.  Secondary  neuron  from  lower  part  of  spinal  V  nucleus  entering  the 
spinal  lemniscus. 

9.  Secondary  netiron  from  chief  sensory  V  nucleus  entering  the  trigeminal 
lemniscus. 

10.  Intrinsic  correlation  neuron  of  thalamus  for  thalamic  reflexes. 

11,  12,  13.  Thalamo-cortical  radiations  to  the  postcentral  gyrus. 


192 


INTRODUCTION    TO    NEUROLOGY 


could  appreciate  all  tactile  stimuli  and  could  localize  accurately 
the  spot  touched  or  pressed  upon.  Yet  it  was  not  possible 
to  produce  pain  anywhere  over  the  right  leg  and  foot  by 
excessive  pressure,  although  he  fully  recognized  its  gradual 
increase.  Referring  to  Fig.  63  (p.  150),  it  is  evident  that  to 
produce  these  symptoms  the  lesion  must  have  involved  the 
conduction  path  for  pain  and  temperature  in  the  lateral 
funiculus  (fiber  8  of  the  figure)  of  the  left  side  of  the  spinal 


Fig.  82. — The  sensory  loss  resulting  from  an  injury  to  the  lower  part  of 
the  spinal  cord.  The  shaded  area  represents  the  parts  insensitive  to  cuta- 
neous painful  stimuli  and  also  to  the  pain  of  excessive  pressure;  yet  over  this 
area  light  touch  and  the  tactile  element  of  pressure  were  appreciated.  (After 
Head  and  Thompson.) 

cord,  and  spared  the  path  for  touch  and  pressure  in  the  ventral 
funiculus  (fiber  9).  Both  superficial  pain  (prick)  and  deep 
pain  caused  by  excessive  pressure  were  abolished.  This 
combination  of  symptoms  could  not  be  produced  by  any 
injury  to  the  nerve-roots  or  peripheral  branches.  For  other 
cases,  see  Spiller  (1915). 

Proprioceptive  Systems. — Referring  back  to  p.  149,  we  are 
reminded  that  the  ascending  proprioceptive  fibers  of  the  spinal 
cord  effect  three  types  of  connections  within  the  brain:  (1)  in 
the  cerebellum;  (2)  in  the  brain  stem;  (3)  in  the  cerebral  cortex. 
The   connections  of  the  second  and  third  types  are  made 


GENERAL    SOMATIC    SYSTEMS    OF   CONDUCTION    PATHS  103 

through  the  dorsal  fimicukis  and  medial  lemniscus;  they  are 
shown  in  Figs.  59,  63,  64,  75,  77,  78,  and  80,  and  in  a  more  com- 
prehensive way  in  Fig.  83. 

The  cortical  proprioceptive  pathway  in  its  simplest  form 
may  consist  of  a  chain  of  only  three  neurons:  (1)  A  peripheral 
neuron  whose  cell  body  lies  in  some  spinal  ganglion,  whose 
dendrite  reaches  some  organ  of  muscle  sense,  tendon  sense,  or 
similar  receptor,  and  whose  axon  terminates  at  the  upper  end 
of  the  cord  in  the  nucleus  of  the  fasciculus  gracilis  or  fasciculus 
cuneatus  of  the  same  side;  (2)  the  body  of  the  second  neuron 
lies  in  one  of  the  nuclei  last  mentioned  (marked  nucleus  of 
dorsal  funiculus  in  Fig.  64),  its  axon  ascends  in  the  medial 
lemniscus,  and  terminates  in  the  lateral  and  ventral  nuclei 
of  the  thalamus  of  the  opposite  side  (Figs.  77  and  83);  (3) 
the  neuron  of  the  third  order  lies  in  the  thalamus  and  sends  its 
axon  through  the  internal  capsule  to  the  somesthetic  area  of  the 
cerebral  cortex. 

The  dorsal  funiculi  of  the  spinal  cord  have  until  recently  been 
regarded  as  the  chief  ascending  pathway  for  all  forms  of 
sensibility,  and  much  of  the  clinical  practice  now  in  vogue  is 
based  upon  this  assumption.  But  evidently  such  an  assump- 
tion is  untenable.  The  dorsal  funiculi  seem  to  be  concerned 
chiefly  with  the  proprioceptive  group  of  reactions.  These  may 
be  unconscious  reflexes  of  motor  coordination  and  the  mainte- 
nance of  equilibrium,  or  they  may  come  into  consciousness  as 
sensations  of  position  and  orientation  of  the  body  and  its 
parts  and  of  spatial  discrimination.  Purely  exteroceptive 
stimuli,  whether  transmitted  by  the  deep  nerves  or  by  the 
cutaneous  nerves,  may  be  carried. for  a  few  segments  in  the 
dorsal  funiculi  (Fig.  81,  neuron  1);  but  they  are  soon  filtered 
off  into  the  gray  matter  of  the  dorsal  column,  and  after  a 
synapse  here  they  are  sorted  into  functionally  distinct  tracts 
on  the  opposite  side  of  the  cord.  The  tactile  elements  of  the 
mixed  peripheral  root  fibers  entering  the  dorsal  funiculus  are 
drawn  off  later  than  are  the  elements  for  thermal  and  painful 
sensibility;  and  some  of  the  components  commonlj^  reckoned 
with  cutaneous  exteroceptive  sensibility  remain  in  the  dorsal 
funiculus  for  its  entire  length.  These  are  chiefly  two-point 
discrimination,  and  discrimination  of  size,  shape,  form,  and 

13 


194 


INTRODUCTION    TO    NEUROLOGY 


5ublhQlamu5/'^-ilijP°'^^^^- 


lateral  lemniscus- 
medial  lemmscu: 


-21.  teclo-cerebellar  TrocT 

— to  -cerebellum 

(brachium  conjunctivum) 


7.  longitudinal    medial 

fasciculus 


dorsol  spino- 
cerebellar  tract,  i- 


to  cerebellunri 
(corpus  resliforme) 


reticular  formation 


^1  medial  lemniscus 

nucleus  of  fasc  gracilis 
nucleus  of  fasc  cuneatus 


e.spino-olivary  troct 

5, ventral  spine-  cerebellar  trad 


Fig.  83. — Diagram  of  the  chief  proprioceptive  conduction  pathways  con- 
tained within  the  spinal  cord  and  brain  stem.  The  mesencephalic  root  of 
the  trigeminal  nerve  (see  p.  197  and  Figs.  71  and  77)  is  omitted  and  not  all 
of  the  cerebellar  connections  are  indicated.  The  connection  to  the  cere- 
bellum from  the  nuclei  of  the  fasciculi  gracilis  and  cuneatus  (neuron  14)  is 
controverted,  but  it  is  well  established  that  similar  connections  are  effected 
immediately  below  this  level  from  the  dorsal  funiculus  of  the  cord.  The 
figure  illustrates  cross-sections  of  the  central  nervous  system  in  the  lower 
cervical  region  of  the  spinal  cord,  at  the  level  where  the  cord  passes  over 


GENERAL    SOMATIC    SYSTEMS    OF    CONDUCTION    PATHS  195 

texture  of  surfaces.  These  all  involve  a  comparison  and  dis- 
crimination in  consciousness  of  spatial  factors  and  arc,  there- 
fore, bound  up  with  those  fibers  which  serve  the  proprioceptive 
reflexes,  which  are  unconscious  spatial  adjustments.  The 
transmission  of  nervous  impulses  of  two-point  discrimination 
(compass  test)  through  the  dorsal  funiculi  rather  than  through 
the  spinal  lemniscus  may  be  correlated  with  the  fact  that  this 
type  of  sensibility  is  a  function  of  the  deep  nerves  (Boring), 
instead  of  the  cutaneous  nerves,  as  taught  by  Head  (see  p.  89). 
Some  peculiar  combinations  of  symptoms  arise  from  the  fact 
that,  whereas  the  ascending  proprioceptive  impulses  (so  far  as 
these  are  consciously  perceived)  pass  up  in  the  dorsal  funiculus 
of  the  same  side  for  the  entire  length  of  the  cord,  the  impulses 
of  the  exteroceptive  impulses,  within  a  few  segments  of  their 
point  of  entrance  into  the  cord,  are  transferred  to  the  opposite 
side  to  ascend  in  the  spinal  lemniscus  tracts.  From  this  it  fol- 
lows that  a  localized  central  injury  involving  the  dorsal  gray 
column  and  dorsal  funiculus  of  one  side  only  will  cut  off  all 
ascending  proprioceptive  impulses  which  pass  through  the  dor- 
sal funiculus  from  lower  levels  on  the  same  side  of  the  body  as 


into   the  medulla  oblongata,  at  the  level  of   the  roots  of  the  VIII  cranial 
nerve,  through  the  inferior  coUiculus,  and  through  the  thalamus. 

1.  Peripheral   neuron   entering   the   dorsal   funiculus    and   also   effecting 
intrinsic  spinal  reflex  connections. 

2.  Peripheral  neuron  entering  the  nucleus  dorsalis  of  Clarke. 

3.  Peripheral  neuron  effecting  connections  with  the  intrinsic  correlation 
neurons  of  the  spinal  cord. 

4.  Peripheral  motor  neurons  of  spinal  nerve. 

5.  Ventral  spino-cerebellar  tract. 

6.  Spino-olivary  tract. 

7.  Dorsal  spino-cerebellar  tract. 

8.  9.  Medial  lemniscus. 

10.  Vestibular  root  fiber  passing  directly  into  the  cerebellum. 

11.  Vestibular  root  fiber  entering  the  vestibular  nucleus. 

12.  Vestibulo-cerebellar  tract. 

13.  Olivo-cerebellar-tract. 

14.  Path  from  the  dorsal  funiculus  (or  its  nuclei)  to  the  cerebellum. 

15.  Path  from  the  reticular  formation  to  the  cerebellum. 

16.  Vestibulo-spinal  tract. 

17.  Path    from    the    vestibular    nucleus    to    the    fasciculus    longitudinalis 
medialis. 

18.  Path  from  the  vestibular  nucleus  to  the  reticular  formation. 

19.  20.  Thalamic  radiations  to  the  cerebral  cortex. 
21.  Tecto-cerebellar  tract. 


196 


INTRODUCTION    TO    NEUROLOGY 


the  lesion,  and  at  the  same  time  will  abolish  both  proprio- 
ceptive and  exteroceptive  functions  in  a  circumscribed  region 
of  the  same  side  of  the  body  whose  exteroceptive  neurons  of 
the  first  order  discharge  into  the  injured  part  of  the  dorsal 
gray  column. 

Figure  84  illustrates  the  loss  of  sensibility  to  painful  stimuli 
resulting  from  a  tumor  in  the  cervical  region  of  the  spinal  cord. 
Tactile,  temperature,  and  deep  sensibility  were  also  profoundly 
disturbed  over  approximately  the  same  region  (the  temperature 
disturbance  involving  the  right  side  also).     These  symptoms 


Fig.  84. — The  loss  of  sensibility  to  pain  resulting  from  a  tumor  in  the  cervica 
region    of    the    spinal    cord.     (After    Head    and    Thompson.) 

resulted  from  the  destruction  of  all  dorsal  root  fibers  in  the 
affected  area  at  the  point  of  their  entrance  into  the  cord  or  of 
the  gray  substance  containing  the  terminals  of  these  fibers,  a 
purely  local  effect.  That  the  dorsal  funiculus  of  the  same  side 
was  also  involved  is  shown  by  symptoms  of  remote  effects  of 
the  injury  in  the  left  foot.  All  forms  of  exteroceptive  sensi- 
bility (touch,  temperature,  pain)  were  perfectly  preserved  in 
both  legs,  but  the  left  leg  was  devoid  of  proprioceptive  sensi- 
bility, as  shown  by  the  loss  of  ability  to  appreciate  the  passive 
position  or  movement  of  the  leg  and  failure  to  discriminate 
two  points  with  the  compass  test. 


GENERAL   SOMATIC    SYSTEMS    OF    CONDUCTION    PATHS  197 

Tlic  intrinsic  connections  within  the  cord  for  spinal  rofloxcs  are  un- 
douhtedl}''  very  i)riniitive.  These  are  both  exteroceptive  and  pro- 
prioceptive in  type  (p.  143).  We  have  seen  that  tlie  ascending  tracts 
between  the  spinal  cord  and  the  brain  fall  into  two  groups:  (1)  The 
exteroceptive  systems  in  the  spinal  lemniscus,  and  (2)  the  projjrioceptive 
systems  in  the  dorsal  funiculus  and  medial  lemniscus.  Comparative 
anatomy  shows  that  the  spinal  lemniscus  system  is  much  older  phy- 
logenetically  than  the  medial  lemniscus  system.  The  fishes  possess 
well-defined  spino-tectal  and  spino-tlialamic  tracts,  but  their  dorsal 
funiculus  possesses  only  the  fasciculus  proprius  fibers  (cf.  Figs.  66,  67, 
pp.  164,  165)  and  they  lack  the  medial  lemniscus  altogether.  The  spino- 
cerebellar tracts,  on  the  other  hand,  are  very  ancient  and  are  present 
from  the  lowest  to  the  highest  vertebrates. 

These  considerations  suggest  that  the  first  fibers  to  pass  from  the  spinal 
cord  to  the  higher  centers  of  the  brain,  and  presumably  the  first  sensory 
impulses  from  the  spinal  nerves  to  be  consciously  perceived,  were  those  of 
touch  and  temperature  transmitted  through  the  spinal  lemniscus.  (Pain 
is  probably  also  very  primitive  as  a  conscious  experience,  but  it  is  doubtful 
w^hether  it  is  represented  in  the  spinal  lemniscus  of  lower  forms;  see  p. 
279).  The  proprioceptive  impulses  in  lower  vertebrates  are  coordinated 
quite  unconsciouslj'  in  the  brain  stem  and  cerebellum,  and  it  is  only  in 
the  higher  forms  that  this  system  of  nervous  impulses  reaches  the 
thalamus  (through  the  medial  lemniscus)  and  cerebral  cortex  for  conscious 
control.  Clinical  evidence  show^s  that  the  medial  lemniscus  connections 
in  man  are  concerned  with  the  conscious  adjustments  of  the  positions 
and  orientation  in  space  of  the  body  and  its  members  and  with  spatial 
discriminations  of  various  sorts,  rather  than  with  the  senses  of  touch  and 
pressure  as  externally  projected.  ■* 

The  innervation  of  the  organs  of  muscular  sensibility  and  tendon  sen- 
sibility in  the  head  is  not  as  fully  known  as  in  the  case  of  those  of  the 
tiimk  and  limbs,  as  above  described.  Sherrington  and  Tozer  have 
recently  show^n  that  such  organs  are  present  in  the  muscles  which  move 
the  eyeball  and  that  their  nerves  accompany  the  motor  fibers  of  the  III, 
IV,  and  VI  cranial  nerves;  but  of  the  central  connections  of  these  sensor j^ 
nerve-fibers  of  the  eye  muscles  nothing  is  known.  It  is  suggested  bj^  the 
researches  of  Johnston,  Willems,  and  many  others  that  the  jaw  muscles, 
which  receive  their  motor  innervation  from  the  motor  V  nucleus  (nucleus 
masticatorius),  receive  their  sensory  innervation  from  the  mesencephalic 
nucleus  of  the  V  nerve,  whose  position  along  the  lateral  border  of  the 
aqueduct  of  Sylvius  is  seen  in  Figs.  71,  75,  and  77.  But  recent  studies  of 
Edgeworth  have  shown  that  these  muscles  also  receive  sensory  fibers  from 
the  semilunar  or  Gasserian  ganglion  of  the  V  nerve,  and  the  question 
requires  further  investigation.  Possiblj'  the  sensory  fibers  from  the 
Gasserian  ganglion  to  the  muscular  branches  of  the  V  nerve  conduct 
impressions  of  deep  sensibility  of  pressure  and  pain  of  the  exteroceptive 
t.vpe,  while  those  from  the  mesencephalic  V  nucleus  innervate  the  muscle 
spindles  for  true  proprioceptive  sensibility. 

The  fibers  of  the  chief  sensory  root  of  the  V  nerve  in  part  end  in  the  chief 
sensory  V  nucleus  near  the  level  of  their  entrance  into  the  medulla 
oblongata  (Figs.  71,  77)  and  in  part  pass  downward  through  the  whole 
length  of  the  medulla  oblongata  and  upper  levels  of  the  spinal  cord  as  the 
spinal  V  tract  (Figs.  64,  71,  72,  81).  It  has  been  suggested  by  compara- 
tive evidence  that  the  spinal  V  tract  and  its  nucleus  are  connected  with  a 


198  INTRODUCTION  TO  NEUROLOGY 

phylogenetically  old  type  of  reaction  to  touch,  temperature,  and  pain, 
probably  chiefly  reflex,  while  the  chief  nucleus  is  concerned  with  the  more 
recently  acquired  discriminations  of  these  systems  with  more  direct 
cortical  connections.  Some  clinical  and  pathological  evidence,  on  the 
other  hand,  suggests  that  the  chief  nucleus  receives  fibers  of  tactile 
sensibility  and  the  spinal  nucleus  the  fibers  of  temperature  and  painful 
sensibility. 1  The  fibers  of  the  trigeminal  lemniscus  (p.  171)  follow 
two  separate  tracts  arising  from  these  two  parts  of  the  sensory 
V  nucleus,  only  the  upper  one  of  which  is  shown  in  Fig.  77,  though 
both  are  shown  in  Fig.  81  (neurons  8  and  9).  The  demonstration  of 
the  course  of  the  trigeminal  lemniscus  fibers  is  very  difficult  and  this 
question  is  in  controversy. 

Motor  Paths, — Throughout  the  length  of  the  spinal  cord  and 
brain  stem  the  ascending  fibers  of  both  exteroceptive  and  pro- 
prioceptive sensibility  give  off  collateral  branches  into  the 
reticular  formation  (p.  172)  for  reflex  connections  with  the 
motor  nuclei  at  various  levels.  The  arrangement  of  these 
motor  nuclei  of  the  brain  stem,  from  which  peripheral  motor 
fibers  of  the  cranial  nerves  arise,  is  shown  on  the  left  side  of 
Fig.  71  (p.  168).  The  details  of  these  connections  for  local 
motor  reflexes  will  not  be  entered  into  here.  From  the  ventral 
part  of  the  thalamus  (p.  178)  there  are  descending  thalamo- 
bulbar  and  thalamo-spinal  tracts  for  local  thalamic  reflexes. 
The  main  descending  pathway  for  voluntary  motor  responses 
to  general  somatic  stimuli  arises  from  the  precentral  gyrus  of 
the  cerebral  cortex  (p.  315).  This  is  the  tractus  cortico-bul- 
baris  (Fig.  75)  and  tractus  cortico-spinalis  or  pyramidal  tract 
(p.  317,  and  Figs.  64,  75,  and  140).  The  reflex  connections 
effected  in  the  medulla  oblongata  are  somewhat  more  com- 
plex than  those  of  the  spinal  cord,  that  is,  they  represent 
the  integration  of  more  different  kinds  of  sensory  impulses 
and  facilitate  the  performance  of  a  greater  variety  of  move- 
ments by  way  of  response.  Similarly,  the  complexity  of  the 
reflex  adjustments  increases  as  we  pass  forward  into  the  mid- 
brain, thalamus,  and  cerebral  cortex  (see  p.  122). 

Attention  has  already  been  called  to  the  fact  that  the  centers  of  ad- 
justment in  the  brain  stem  are  of  two  physiologically  different  types  which 
we  have  termed  centers  of  correlation  and  centers  of  coordination  (p.  36). 
The  more  labile  and  individually  variable  adjustments  are  effected  in 
the  correlation  centers  which  are  developed  from  the  more  dorsal  parts 
of  the  embryonic  neural  tube  above  the  limiting  sulcus  (p.  129),  while  the 

^  Spillek,  W.  G.  1915.  Remarks  on  the  Central  Representation  of 
Sensation,  Jour.  Nerv.  and  Ment.  Dis.,  vol.  xlii,  pp.  399-418. 


GENERAL    SOMATIC    SYSTEMS    OF    CONDUCTION    PATHS  199 

more  ventral  parts  of  the  neural  tube  give  rise  to  the  motor  centers  and 
the  centers  of  coordination,  whose  adjustments  are  of  a  more  fixed  and 
invariable  character.  In  the  embryonic  development  the  coordination 
centers  develop  precociously,  while  the  correlation  centers  mature  more 
slowly ;  the  higher  association  centers  of  tlie  thalamus  and  cerebral  cortex 
in  particular  are  the  last  to  mature  (p.  320). 

In  the  phylogenetic  development  of  the  brain  the  same  rule  holds. 
In  the  lowest  vertebrates  the  coordination  centers  are  much  larger  in 
proportion  to  the  size  of  the  correlation  centers  than  in  higher  verte- 
brates. Bartelmez^  has  analyzed  these  motor  coordination  mechanisms 
(which  he  terms  in  the  aggregate  the  nucleus  motorius  tegmenti)  in 
fishes,  and  finds  in  the  motor  tegmentum  throughout  the  medulla 
oblongata  a  nucleus  of  a  primitive  type  whose  neurons  serve  to  connect 
the  primary  sensory  nuclei  with  the  primary  motor  nuclei.  Some  of 
these  connections  are  very  short,  while  others  are  very  long,  reaching 
remote  parts  of  the  brain  and  spinal  cord  through  the  longitudinal  medial 
fasciculus  (pp.  203,  235).  This  nucleus  is  the  parent  tissue  out  of  which 
the  more  complex  coordination  centers  in  the  tegmentum  of  higher 
vertebrates  have  been  differentiated. 

In  very  young  amphibian  embryos  CoghilP  finds  a  still  simpler  con- 
dition which  is  probably  also  more  primitive.  In  the  spinal  cords  of 
these  larvae  the  individual  neurons  of  the  motor  tegmentum  give  rise 
both  to  fibers  of  the  longitudinal  conduction  tract  of  motor  coordination 
(fasciculus  proprius  ventralis)  and  to  peripheral  fibers  of  the  ventral 
roots,  the  latter  arising  as  collaterals  of  the  longitudinal  axons.  Ii* 
older  larvae  separate  neurons  have  been  differentiated  for  these  two  func- 
tions of  peripheral  conduction  and  longitudinal  conduction.  The  steps 
in  the  embryologic  development  and  probable  evolution  of  the  more 
complex  centers  of  adjustment  have  been  briefly  reviewed  by  Herrick 
and  Coghill  (see  pp.  71,  122). 

Summary. — The  old  clinical  concept  ''general  sensibility" 
has  recently  been  analyzed  into  a  number  of  components,  the 
most  fundamental  division  being  the  distinction  between  a 
group  of  exteroceptive  and  a  group  of  proprioceptive  systems. 
The  exteroceptive  systems  are  transmitted  from  the  spinal 
cord  to  the  brain  through  a  complex  tract,  the  spinal  lemniscus, 
within  which  there  are  separate  pathways  for  the  three  quali- 
ties of  sensation,  touch,  temperature,  and  pain.  These  sensa- 
tion qualities  come  into  consciousness  with  a  distinct  peripheral 
or  external  reference.     The  proprioceptive  systems   (muscle 

1  Bartelmez,  G.  W.  1915.  Mauthner's  Cell  and  the  Nucleus 
Motorius  Tegmenti,  Jour.  Comp.  Neur.,  vol.  xxv,  pp.  87-128. 

2  Coghill,  G.  E.  1913.  The  Primary  Ventral  Roots  and  Somatic 
Motor  Column  of  Amblj^stoma,  Jour.  Comp.  Neur.,  vol.  xxiii,  pp. 
121-144. 

— .  1914.  Correlated  Anatomical  and  Physiological  Studies  of  the 
Growth  of  the  Nervous  Sj^stem  of  Amphibia,  Jour.  Comp.  Neur.,  vol. 
x.xiv,  pp.  161-233. 


200  INTRODUCTION  TO  NEUROLOGY 

sense  and  allied  types)  are  transmitted  to  the  brain  through 
the  dorsal  funiculus  of  the  same  side  of  the  cord,  the  medial 
lemniscus  of  the  opposite  side,  the  thalamus,  and  the  somes- 
thetic  radiations  to  the  cerebral  cortex;  and  also  through  the 
spino-eerebellar  tracts  to  the  cerebellar  cortex.  Most  of  these 
reactions  of  spatial  adjustment  do  not  come  into  consciousness 
at  all,  but  some  appear  subjectively  as  sensations  of  posture, 
bodily  movement,  and  spatial  discrimination.  The  cerebellum 
is  the  great  clearing  house  for  these  and  all  other  afferent  sys- 
tems which  are  concerned  in  the  proprioceptive  functions,  so 
far  as  these  are  unconsciously  performed 


CHAPTER  XII 
THE  VESTIBULAR  APPARATUS  AND  CEREBELLUM 

The  general  somatic  sensory  systems  considered  in  the  last 
chapter  include  some  of  the  most  primitive  reflex  mechanisms. 
These  fall  into  two  groups — the  exteroceptive  systems  and  the 
proprioceptive  systems  (pp.  82-93) — and  each  of  these  groups 
comprises,  in  addition  to  its  primitive  generalized  members, 
certain  so-called  organs  of  special  or  higher  sense.  The  special 
exteroceptive  sense  organs  are  the  organ  of  hearing  (p.  217) 
and  the  organ  of  vision  (p.  228).  The  special  proprioceptive 
sense  organs  are  the  semicircular  canals  of  the  internal  ear; 
and  those  will  next  be  described,  together  with  their  central 
mechanisms  in  the  medulla  oblongata  and  cerebellum. 

The  Vestibular  Apparatus. — The  internal  ear  contains  two 
quite  distinct  groups  of  sense  organs,  the  organ  of  hearing  in 
the  cochlea  and  the  vestibular  organs  (utricle,  saccule,  and 
semicircular  canals),  both  of  which  are  suppUed  by  the  VIII 
cranial  nerve,  which  accordingly  has  two  parts,  the  cochlear 
and  the  vestibular  nerves.  The  semicircular  canals  are  the 
most  highly  specialized  end-organs  of  the  proprioceptive  series 
and  are  concerned  chiefly  with  the  maintenance  of  bodily  equi- 
librium. The  general  structure  of  the  internal  ear  is  described 
on  p.  .217;  here  we  need  merely  mention  that  the  three  semi- 
circular canals  (ductus  semicirculares)  of  each  ear  lie  approxi- 
mately at  right  angles  to  each  other,  as  shown  diagrammatic- 
ally  in  Fig.  85,  and  each  canal  is  dilated  at  one  end  to  form  the 
ampulla,  within  which  is  a  patch  of  sensory  epithelium  from 
which  hairs  project  into  the  contained  fluid  (see  Figs.  32  and 
91).  A  movement  of  the  head  in  any  direction  will  cause 
stimulation  of  the  sensory  cells  in  one  or  more  of  these  canals 
in  each  ear,  which  in  turn  will  excite  a  nervous  impulse  in  the 
nerve  supplying  the  corresponding  ampullae.  These  nervous 
impulses  will  be  transmitted  to  the  vestibular  centers  of  the 

201 


202 


INTRODUCTION    TO    NEUROLOGY 


brain,  where  they  will  be  so  analyzed  as  to  call  forth  the  ap- 
propriate reaction  to  the  movement  which  has  excited  the 
particular  semicircular  canals  involved. 

The  fibers  of  the  vestibular  nerve  enter  the  medulla  oblon- 
gata immediately  behind  the  pons  and  terminate  in  a  vestibular 
nucleus  which  forms  an  eminence  on  the  floor  of  the  fourth 


Fig.  85. — Diagram  of  the  position  of  the  semicircular  canals  in  the  head, 
as  seen  from  behind.  On  each  side  it  will  be  seen  that  the  three  canals  lie 
in  planes  at  right  angles  to  one  another.  The  external  or  horizontal  canals 
(E)  of  the  two  sides  lie  in  the  same  plane.  The  anterior  canal  of  one  side 
(A)  lies  in  a  plane  parallel  to  that  of  the  posterior  canal  (P)  of  the  other 
side.     (After  Ewald.) 

ventricle  in  this  region  (Figs.  71,  96).     This  nucleus  has  four 
subdivisions,  as  follows: 

Nucleus  nervi  vestibuli  medialis  (of  Schwalbe,  also  called  nucleus 
dorsalis,  triangular  nucleus  and  principal  nucleus). 

Nucleus  nervi  vestibuli  lateralis  (of  Deiters,  also  called  nucleus  mag- 
nocellularis). 

Nucleus  nervi  vestibuli  superior  (of  Bechterew). 

Nucleus  nervi  vestibuli  spinalis. 

The  arrangement  of  these  nuclei  and  of  some  of  their  second- 
ary connections  is  shown  in  Fig.  86.  Some  of  these  connections 
are  made  with  the  motor  nuclei  and  reticular  formation  of  the 


THE   VESTIBULAR   APPARATUS    AND    CEREBELLUM 


203 


medulla  oblongata  for  local  bulbar  reflexes ;  there  is  a  vestibulo- 
spinal tract  (tr.v.sp.)  for  movements  of  the  trunk  and  limbs 


Fig.  86. — Diagram  of  the  nuclei  of  the  vestibular  nerve,  together  with 
some  of  the  associated  fiber  tracts.  The  secondary  tracts  associated  with 
the  vestibular  nuclei  are  drawn  in  full  lines;  a  part  of  the  secondary  auditory 
path  from  the  cochlear  nuclei  is  drawn  in  broken  lines.  Compare  Figs. 
71,  77,  96.  br.c.inf.,  brachium  quadrigeminum  inferius;  c.g.m.,  corpus  genicula- 
tum  mediale;  collie,  inf.,  coUiculus  inferior;  collie,  sup.,  colliculus  superior; 
f.l.m.,  fasciculus  longitudinalis  medialis;  L,  nucleus  nervi  vestibuli  lateralis 
(Deiters);  Im.  lat.,  lemniscus  lateralis;  M,  nucleus  nervi  vestibuli  medialis 
(Schwalbe);  n.lm.  lat.,  nucleus  of  lemniscus  lateralis;  ??mc.  amb.,  nucleus 
ambiguus;  ol.  sup.,  superior  olive;  S,  nucleus  nervi  vestibuli  superior  (Bech- 
terew) ;  Sp.,  nucleus  spinalis  nervi  vestibuli;  tr.  v.  cereb.,  tractus  vestibulo- 
eerebellaris;  tr.v.sp.,  tractus  vestibulo-spinalis;  VIII  c,  radix  cochlearis  of 
VIII  nerve;  VIII  v.,  radix  vestibularis  of  VIII  nerve. 

in  response  to  stimulation  of  the  semicircular  canals;  and  there 
is  also  a  strong  connection  \\ith  the  longitudinal  medial  fascicu- 


204  INTRODUCTION  TO  NEUROLOGY 

lus  (f.l.m.),  by  which  fibers  descend  to  the  spinal  cord  (chiefly 
for  turning  movements  of  the  head  by  the  neck  muscles)  and 
ascend  to  the  midbrain.  The  last-mentioned  fibers  connect 
chiefly  with  the  nuclei  of  the  motor  nerves  for  the  eye  muscles 
(III,  IV,  and  VI  pairs  of  cranial  nerves),  thus  providing  for 
the  conjugate  movements  of  the  eyes  which  accompany  head 
movements  (in  this  way,  for  instance,  enabling  one  to  keep  the 
gaze  fixed  upon  a  stationary  object  while  the  head  is  moving, 
cf.  p.  235). 

It  will  be  noticed  that  there  is  no  important  pathway  from 
the  vestibular  nucleus  to  the  thalamus  and  cerebral  cortex,  for 
the  equilibratory  reactions  excited  from  the  semicircular  canals 
are  normally  unconsciously  performed.  This  is  in  marked 
contrast  with  the  connections  of  the  cochlear  nerve,  for  the 
auditory  reactions  are  often  consciously  directed  (p.  222). 
There  is,  however,  an  important  connection  with  the  cerebel- 
lum, partly  directly  by  root  fibers  of  the  vestibular  nerve  and 
partly  by  secondary  fibers  from  the  superior  and  lateral  vestibu- 
lar nuclei  (Fig.  86).  The  cerebellum  is,  accordingly,  an  im- 
portant center  of  adjustment  for  the  proprioceptive  reflexes, 
and  to  this  our  attention  will  next  be  directed. 

The  Cerebellum. — This  important  organ  is  an  overlord 
which  dominates  the  proprioceptive  functions  of  the  body  in 
somewhat  the  same  way  that  the  cerebral  cortex  directs  and 
controls  the  exteroceptive  reactions.  Both  of  these  organs  are 
secondarily  added  to  the  more  primitive  segmental  structures 
of  the  brain  stem,  that  is,  they  are  suprasegmental  (p.  122). 

The  correlation  centers  of  the  brain  stem,  and  particularly 
those  of  the  cerebral  cortex,  analyze  the  afferent  impulses 
entering  the  brain  and  determine  what  particular  reactions  are 
appropriate  in  each  situation.  After  the  character  of  the 
movement  has  been  determined  in  this  way,  the  proprioceptive 
systems  cooperate  in  its  execution,  and  the  cerebellum  is  the 
central  coordination  station  for  the  proprioceptive  reactions. 
None  of  its  activities  come  into  consciousness. 

The  cerebellum,  therefore,  is  intimately  connected  with  all 
sensory  centers  which  are.  concerned  in  the  adjustment  of  the 
body  in  space  and  motor  control  in  general.  The  maintenance 
of  muscular  tone  and  of  bodily  equilibrium   are  the  most 


THE   VESTIBULAR    APPARATITS    AND    CEREBELLUM 


205 


important  of  these  functions,  and  tlie  semicircular  canals  of 
the  internal  ear  (pp.  93,  218)  are  the  receptive  organs  which 


(^erebelfum 


Tr  olivo<ereb. 

tr.spino- 
cereb.  doi'S. 

(Flechsig] 


Tv  spino-olivari5' 
tr  coi^tico-spinalis' 


brachium 
conjuricrivum 
-Tk;  tecto-cereb. 
tr  ponto-cereb. 
mesencephalon 


central 

tegmental 

troct. 

tr.  cortico- 
olivQ  inferior  pontili's 

tr  spino  -  cereb  ventr.   (Gowers) 


Fig.  87,  A. — Diagram  of  the  chief  afferent  tracts  leading  into  the  cerebellum. 


cerebel/ufT? 


nuc.  dentatu 

roof  nuclei 

corpus  restiforme 


.brachium    pontis 

brachium 

conjuncTivum 

tr  cereb.-tegmenTalis 
mesencephaii 


■mesencephalon 

bro.  thai. 


.-.  rubro- 

5pinalis 

Tr  cerebello- 

tegmentalis 

pontis 

tr.  cerebello-tegmentalis   buibi 
Fig.  S7,  B. — Diagram  of  the  chief  efferent  tracts  leading  out  of  the  cerebellum. 

are  of  chief  impoitance  in  these  reactions.     Comparative  and 
embryological  studies  show  that  the  cerebellum  was  developed 


206  INTRODUCTION  TO  NEUROLOGY 

as  a  direct  outgrowth  from  the  primary  centers  for  the  semi- 
circular canals  in  the  medulla  oblongata  (the  acoustico- 
lateral  area  of  fishes,  Fig.  43,  cf.  Herrick,  1914),  and  even  in  the 
human  body  root  fibers  from  the  vestibular  branch  of  the 
VIII  cranial  nerve  enter  the  cerebellum  directly.  Neurons 
of  the  second  order  also  enter  the  cerebellum  from  the  ves- 
tibular nucleus,  as  well  as  from  the  spinal  cord  and  from  prac- 
tically all  of  the  somatic  sensory  centers  of  the  brain ;  there  is 
also  a  very  important  path  from  the  cerebral  cortex  by  way 
of  the  pons. 

The  cerebellum  is  attached  to  the  brain  stem  by  three 
stalks  or  peduncles  on  each  side,  the  superior  peduncle 
(brachium  conjunctivum),  the  middle  peduncle  (brachium 
pontis) ,  and  the  inferior  peduncle  (corpus  restif orme) .  Figure 
87,  A  illustrates  diagrammatically  the  chief  pathways  which 
enter  the  cerebellum,  and  Fig.  87,  B  those  by  which  nervous 
impulses  leave  it.  We  cannot  here  describe  these  connec- 
tions in  detail  but  can  mention  a  few  only  of  their  general 
features. 

The  cerebellum,  as  already  stated,  receives  afferent  im- 
pulses from  all  of  the  important  somatic  sensory  centers  and 
also  from  the  cerebral  cortex.  The  afferent  fibers  from  the 
spinal  cord  and  brain  stem  enter  by  the  superior  and  inferior 
peduncles.  The  pons  is  an  eminence  under  the  upper  part 
of  the  medulla  oblongata  (Fig.  53)  which  contains  gray  centers 
(the  pontile  nuclei).  Fibers  pass  into  the  pontile  nuclei  from 
the  association  centers  of  the  cerebral  cortex  by  way  of  the 
cortico-pontile  tracts,  and  from  the  motor  areas  of  the  cerebral 
cortex  by  way  of  collateral  branches  from  the  cortico-spinal 
tract  as  it  passes  through  the  pons.  These  nervous  impulses 
enter  the  cerebellar  hemispheres  from  the  pons  by  the  middle 
cerebellar  peduncles. 

Fibers  leave  the  cerebellum  by  all  three  peduncles  for  the 
motor  centers  of  the  brain  stem  (the  cerebello-tegmental  tracts, 
Fig.  87,  B),  and  a  much  larger  number  leave  by  the  superior 
peduncle  for  the  red  nucleus  (nucleus  ruber.  Fig.  75)  and 
adjacent  parts  of  the  brain  stem,  these  fibers  first  crossing  to 
the  opposite  side  of  the  brain  in  the  cerebral  peduncle  under 
the  aqueduct  of  Sylvius.     From  the  red  nucleus  fibers  pass 


THE   VESTIBULAR    APPARATrS    AND    CEREBELLUM  207 

downward  into  the  spintd  cord  (rid)ro-spinal  tract)  and  upward 
to  the  cerebral  cortex. 

Many  of  the  tracts  connecting  with  the  cerebellum  are  uncrossed,  thus 
differing  from  those  of  the  cerebral  cortex  which  are  all  made  with  the 
opposite  side  of  the  body.  The  symptoms  of  local  injury  of  one  cerebral 
hemisphere  are,  accordingly,  usually  manifested  on  the  opposite  side  of 
the  body  from  the  lesion,  while  the  symptoms  of  cerebellar  disease  are 
generally  obscurely  localized  or  are  manifested  on  the  same  side  as  the 
lesion.  But  some  of  the  cerebellar  connections  are  crossed  and  others, 
like  the  dorsal  spino-cerebellar  and  vestibulo-cerebellar  tracts,  which 
enter  the  cerebellum  uncrossed  may  effect  connection  with  the  opposite 
side  within  the  substance  of  the  cerebellum.  The  following  cerebellar 
tracts  decussate  outside  the  cerebellum: 

The  olivo-cerebellar  tract  arises  from  the  inferior  olive,  crosses  to  the 
opposite  side  in  the  interolivary  space,  penetrates  the  other  olive  with- 
out effecting  functional  connection  with  it,  and  then  enters  the  cere- 
bellum through  its  inferior  peduncle  (Figs.  72  and  87,  ^4).  The  cerebral 
cortex  sends  large  descending  cortico-pontile  tracts  to  the  pons  of  the 
same  side  (Figs.  75  and  87,  A).  Here  there  is  a  synapse  in  the  pontile 
nuclei,  whose  neurons  discharge  into  the  opposite  cerebellar  hemisphere 
through  the  tractus  ponto-cerebellaris  in  the  middle  cerebellar  peduncle. 
The  efferent  path  from  the  cerebellum  to  the  red  nucleus  contained  with- 
in the  superior  cerebellar  peduncle  decussates  in  the  cerebral  peduncle 
before  entering  the  red  nucleus.  Important  evidence  regarding  these 
decussations  and  the  connections  of  the  cerebellum  with  the  brain  stem 
in  general  is  furnished  by  a  case  of  defective  development  of  the  cere- 
bellum on  one  side  described  by  Strong  (1915). 

The  connections  just  described  illustrate  some  of  the 
pathways  by  which  the  cerebellum  is  able  to  reinforce,  co- 
ordinate, or  otherwise  modify  the  somatic  motor  mechanisms. 
There  is  an  immense  amount  of  potential  nervous  energy 
always  available  in  the  neurons  of  the  cerebellar  cortex,  and 
the  cerebellum  appears  to  be  constantly  exerting  a  stimulating 
or  tonic  effect  upon  the  body  muscles.  An  injury  to  the 
cerebellum  (especially  an  unsymmetric  lesion)  produces 
motor  incoordination,  and  the  total  removal  of  the  cerebellum 
results  in  loss  of  muscular  tone  and  great  weakness,  though 
there  is  no  abolition  of  any  particular  motor  functions.  The 
cerebellar  cortex  and  the  cerebral  cortex  are  very  intimately 
connected  by  large  fiber  tracts,  and  each  apparently  exerts 
an  important  physiological  effect  upon  the  other.  But  the 
exact  nature  of  this  reciprocal  control  is  still  obscure. 

The  cerebellar  cortex  differs  from  the  cerebral  cortex  in  the 
form  and  arrangement  of  its  neurons  and  also,  further,  in  that 


208  INTRODUCTION  TO  NEUROLOGY 

it  is  structurally  similar  throughout  its  entire  extent.  The 
cerebral  cortex,  on  the  other  hand,  shows  differences  in  the 
forms  and  arrangements  of  its  neurons  in  different  regions,  and 
this  is  correlated  with  a  regional  localization  of  diverse  func- 
tions (pp.  303,  314).  There  is  some  evidence  that  different 
parts  of  the  cerebellar  cortex  exert  a  dominant  regulatory- 
influence  over  particular  large  groups  of  muscles;  but  this 
localization  of  function  is  of  a  very  general  sort  and  is  by  no 
means  so  precise  as  the  localization  of  voluntary  motor  centers 
in  the  cerebral  cortex.  Moreover,  the  physiological  influence 
of  the  cerebellum  upon  movement  is  of  a  very  different  sort 
from  that  of  the  cerebral  cortex. 

The  mammalian  cerebellum  consists  of  a  median  lobe, 
the  worm  (vermis),  and  two  larger  cerebellar  hemispheres. 
The  vermis  alone  is  well  developed  in  lower  vertebrates 
(from  fishes  to  birds,  see  Fig.  43,  p.  119).  In  different  mam- 
mals the  size  of  the  pons  and  brachium  pontis  is  proportional 
to  that  of  the  cerebellar  hemispheres,  and  all  of  these  vary 
in  proportion  to  the  size  of  the  cerebral  cortex.  The  pons 
and  cerebellar  hemispheres,  therefore,  are  in  a  general  way 
dependencies  of  the  cerebral  cortex  (see  p.  122),  and  prob- 
ably are  concerned  chiefly  with  the  coordination  of  vol- 
untarily excited  movements.  These  voluntary  acts,  however, 
do  not  differ  on  the  motor  side  from  similar  movements  which 
are  reflexly  excited ;  and  in  the  actual  functioning  of  the  human 
cerebellum  it  is  probable  that  its  control  of  motor  coordination 
is  quite  independent  of  the  mode  of  excitation  of  the  move- 
ments— whether  reflex  or  voluntary.  In  other  words,  the 
anatomical  distinction  between  vermis  and  cerebellar  hemi- 
spheres has  very  limited  physiological  significance.  This 
applies  especially  to  the  superior  part  of  the  cerebellum.  The 
inferior  part  of  the  vermis,  as  we  shall  see,  has  more  physio- 
logical individuality. 

The  comparative  anatomy  and  comparative  embryology  of 
the  cerebellum  have  recently  been  carefully  studied  by  Elliot 
Smith,  Bolk,  and  Rynberk.  They  have  shown  that  its 
anatomical  subdivisions,  as  named  by  the  B.  N,  A.  have  no 
especial  significance.  The  nomenclature  of  the  B.  N.  A.  and 
of  Bolk  and  some  other  students  are  contrasted  in  Fig.  88. 


THE   VESTIBULAR    APPARATUS    AND    CERF:BELLUM  209 

By  fjomparing  the  sizes  and  arrangement  of  the  parts  of  the 
cerebellum,  as  Bolk  enumerates  them,  in  various  animals 
with  different  modes  of  life  this  author  concludes  that  there 
are  coordination  centers  in  the  cerebellum  for  particular 
groups  of  muscles,  whose  arrangement  in  man  is  represented 
in  Fig.  88. 

Van  Rynberk  and  Andre-Thomas  and  Durupt  tested  the 
truth  of  this  conclusion  experimentally  by  extirpating  these 
areas  in  animals  and  observing  the  resulting  symptoms, 
finding  that  Bolk's  scheme  in  general  is  correct.  Barany  and 
other  clinical  neurologists  by  observing  the  symptoms  re- 
sulting from  localized  lesions  of  the  human  cerebellum  have 
been  led  to  similar  conclusions. 

As  a  result  of  these  studies  we  conclude  that  the  distinction 
between  vermis  and  cerebellar  hemispheres  in  general  has 
little  physiological  significance.  The  most  important  land- 
mark in  the  cerebellum  is  Bolk's  sulcus  primarius  (the  fissura 
prima  of  Elliot  Smith)  which  separates  a  lobus  anterior  from 
a  lobus  posterior,  the  former  being  an  unpaired  center  for  the 
control  of  movements  of  the  head.  Behind  the  sulcus  prim- 
arius on  the  dorsal  surface  is  the  lobulus  simplex,  a  similar 
unpaired  center  for  movements  of  the  neck.  Behind  this 
is  a  median  center  for  the  control  of  bilateral  movements  of  the 
limbs  (the  tuber  vermis  of  the  B.  N.  A.,  Fig.  88,  C).  Along 
the  caudal  and  inferior  faces  of  the  cerebellum  is  a  median 
center  for  movements  of  the  trunk  (pyramis,  uvula  and  nodu- 
lus  of  the  B.  N.  A.),  This  is  largely  concerned  with  move- 
ments of  equilibration.  In  the  cerebellar  hemisphere  of  each 
side  is  a  center  for  the  control  of  unilateral  movements  of  the 
limbs.  The  arm  area  is  on  the  dorsal  and  caudal  surface. 
The  leg  area  in  man  has  not  been  clearly  determined,  but  by 
analogy  with  other  mammals  it  probably  lies  as  indicated  in 
Fig.  88,  B.  The  paramedian  lobule  (tonsilla  of  the  B.  N.  A.) 
and  the  flocculus  together  form  the  formatio  vermicularis 
and  in  lower  mammals  apparently  are  concerned  with  tail 
movements.     Their  significance  in  man  is  obscure. 

This  functional  localization  is  in  the  cerebellar  cortex. 
From  what  we  know  of  the  fiber  connections  of  the  cerebellar 
cortex  it  may  be  inferred  that  the  dentate  nucleus  is  largely 

14 


210 


INTRODUCTION    TO    NEUROLOGY 


concerned  with  tlie  coordination  of  movements  of  the  arm 
and  hand  of  the  same  side,  while  the  roof  nuclei  in  the  inferior 


B.  N.  A. 
Ala  lobuli    centralis 

Lobulus    centralis 

Culmen  monticuli 
Pars  anterior  lobuli 

quadrangularis 
Pars  posterior  lobuli 

quadrangularis 

Declive  monticuli 

Lobulus  semilunaris 

superior 


Lobulus  centralis 
Ala    lobuli  centralis 

Brachium  pontis 

Flocculus 

Brachium 

conjunctivum 

Nodulus 

Uvula 

Tonsilla 

Lobulus  biventer 
Pyramis 
Tuber 
Lob.  semilun.   inf. 
Sulcus      horizontalis 
Lubulus  semilu- 
naris superior 


BOLK 
Lobus  anteri 


Sulcus  primarius 
Lobulus  simplex 
S.  pel. 
Lobulus  ansiformis 


Lobus  anterior 

Cerebellar  pedun- 
cles (cut) 
Flocculus 
Sulcus 

uvulo-nodularis 
Lobulus 
paramedianus 
Fissura  secunda 


Lobulus 
ansiformis 


Fig.  88,  B. — The  human   cerebellum   from   below. 

In  these  two  diagrams  the  principal  subdivisions  of  the  cerebellum  are 
indicated  and  the  B.  N.  A.  names  are  designated  at  the  left.  At  the  right 
are  the  names  given  by  Bolk  to  these  structures  and  one  fissure  not  named 
by  Bolk,  the  sulcus  postclivalis  (S.pcl.),  as  named  by  Symington  in  Quain's 
Anatomy.  The  sulcus  primarius  of  Bolk  and  Kuithan  is  the  same  as  the 
furcal  sulcus  of  Stroud,  the  fissura  prima  of  Elliot  Smith,  and  the  sulcus 
preclivalis  of  Symington.  The  lobulus  simplex  of  Bolk  extends  across  the 
median  plane  and  includes  the  declive  of  the  B.  N.  A.  in  the  vermis. 

The  functional  localization  within  the  cerebellar  cortex  as  determined 
by  Bolk,  Rynberk,  and  others  is  also  indicated  on  the  figures.  Head  move- 
ments are  controlled  in  the  lobus  anterior  of  Bolk,  i.  e.,  all  parts  in  front  of 
the  sulcus  primarius.  The  lobus  simplex  controls  neck  movements.  Arm 
and  leg  movements  are  controlled  in  the  lobus  ansiformis  and  trunk  movements 
in  the  inferior  vermis. 

vermis  are  concerned  with  bilateral  movements,   especially 
those  concerned  with  equilibration. 

The  similarity  of  structure  throughout  the  cerebellar 
cortex,  in  contrast  with  the  diversity  in  the  cerebral  cortex, 


THE   VESTIBULAR    APPARATUS    AND    CEREBELLUM 


211 


suggests  that  the  nature  of  cerebellar  function  is  essentially 
similar  throughout  and  that  the  functional  localization  de- 


Foliuin  vermis 
Declive  monticuli 


Culmen  monticuli 


Velum 


er  vermis 


Lobulus  centralis 


Uvula 

Nodulut* 

Tela  chorioidea 
ventriculi  quarti 


Lingula 


Fig.  88,  C. — A  sagittal  section  through  the  vermis  of  the  human  cerebel- 
lum. The  B.  N.  A.  names  of  the  parts  arc  given  and  also  the  functional 
localization  as  determined  by  Bolk,  Rynberk,  and  others.  The  areas  of 
the  head  and  neck  extend  lateralward  as  indicated  on  Fig.  88,  A.  The  area 
for  control  of  movements  of  the  trunk  is  limited  to  the  inferior  vermis. 
The  area  for  the  limbs  in  the  tuber  vermis  is  for  the  control  of  coordinated 
movements  of  both  members  of  a  pair,  while  the  arm  and  leg  areas  shown 
in  Figs.  88  ,  A  and  88,  B  control  the  separate  movements  of  these  limbs. 


r^  V      Fissura  secunda 


Sulcus 
uvulo-nodularis 

S.  preen. 

Fig.  88,  D. — The  same  section  .shown  in  Fig.  88,  C  with  the  names  of  the 
cerebellar  fissures.  Bolk's  names  are  printed  in  full;  others  are  abbre- 
viated. Between  the  lingula  and  the  lobus  centralis  is  the  sulcus  prc- 
centralis  (S. preen.)  of  Symington.  Above  the  lobtilus  centralis  is  the  sulcus 
postcentralis  (S.pcen.)  of  Symington,  or  fissura  preculminata  of  Elliot 
Smith.  The  sulcus  primarius  of  Bolk  is  the  fissura  prima  of  Elliot  Smith 
and  the  sulcus  preclivalis  of  Sj'mington.  Above  the  declive  is  the  sulcus 
postclivalis  (S.pcl.)  of  Symington.  Between  the  folium  and  the  tuber  is 
the  sulcus  horizontalis  magnus  (S.h.m.)  of  Symington.  Between  the  tuber 
and  the  pyramis  is  the  sulcus  postpyramidalis  {S.npy.)  of  Symington.  Below 
the  pyramid  is  the  fissura  secunda  of  Bolk  ana  Elliot  Smith,  or  stilcus  pre- 
pyramidalis  of  Symington.  Between  the  uvula  and  the  nodulus  is  the 
sulcus  nvulo-nodularis  of  Bolk  or  sulcus  postnodularis  of  Symington. 

scribed  is  determined  simply  by  differences  in  the  lower  motor 
centers  with  which  the  various  cerebellar  regions  are  connected. 


212 


INTRODUCTION    TO    NEUROLOGY 


The  surface  of  the  cerebellum  is  divided  by  deep  fissures  or 
sulci  into  narrow  leaf-like  subdivisions  termed  folia  or  gyri, 
so  that  when  it  is  cut  open  across  the  median  plane  the  cut  sur- 
face looks  somewhat  like  a  sprig  of  the  common  evergreen  cedar 


Fig.  89. — Semidiagrammatic  section  taken  transversely  through  a  folium 
of  the  cerebellar  cortex  (Golgi  method):  A,  molecular  layer,  filled  with 
axons  of  graniile  cells  cut  at  right  angles  to  their  course;  B,  granular  layer;  C, 
white  matter;  a,  Purkinje  cell,  with  the  dendrite,  broadly  spread  out  in 
the  transverse  plane  (compare  Fig.  15);  b,  basket  cell  (compare  Fig.  16); 
d,  terminal  arborizations  of  the  basket  cells  enveloping  the  bodies  of  the 
Purkinje  cells;  e,  superficial  stellate  cells;  /,  Golgi  cell  of  type  II  (see  p. 
45) ;  g,  granule  cells  with  their  axons  ascending  and  bifurcating  in  the  mole- 
cular layer  at  i]  h,  mossy  fibers;  i,  neuroglia  cell;  m,  neuroglia  cell;  n,  climbing, 
fibers.     (After  Ramon  y  Cajal.) 

tree  know  as  arbor  vitse.     Hence  this  cut  surface  by  the  an- 
cients was  termed  the  arbor  vitse. 

The  gray  matter  of  the  cerebellum  is  partly  superficial  (this 
is  the  cortex  to  which  reference  has  already  been  made)  and 


THE   VESTIBULAR    APPARATUS    AKD    CEREBELLUM  213 

partly  in  llic  foiiu  of  deep  nuclei  embedded  within  the  white 
matter.  The;  largest  of  these  deep  gray  centers  arc;  the  dentate 
nuclei  within  the  cerebellar  hemispheres.  Within  the  vermis 
are  other  smaller  centers,  called  the  roof  nuclei,  because  they  lie 
immediately  above  the  fourth  ventricle  (nuclei  emboliformis, 
globosus,  and  fastigii,  see  Fig.  96).  Some  of  the  afferent  fibers 
which  enter  the  cerebellum  end  in  these  nuclei,  but  most  of 
them  end  in  the  cortex.  The  efferent  fibers,  on  the  other  hand, 
arise  from  the  deep  nuclei,  especially  the  dentate  nuclei 
(Fig.  87,5). 

The  cerebellar  cortex  has  three  distinct  layers.  External  to 
the  central  white  matter  (Fig.  89,  C)  is  a  wide  layer  composed 
of  very  minute  granule  cells  (Fig.  89,  B)  densely  crowded 
together,  with  scanty  cytoplasm,  short,  claw-like  dendrites, 
and  slender  unmyelinated  axons  which  ascend  to  the  superficial 
molecular  layer  (Fig.  89,  A),  where  they  bifurcate  (their 
branches  running  lengthwise  of  the  folium)  and  end  among 
the  dendrites  of  the  Purkinje  cells,  to  be  described  immedi- 
ately. The  middle  layer  of  the  cortex  is  composed  of  a  single 
row  of  Purkinje  cells  (Fig.  89,  a);  these  have  large  globose 
bodies  with  massive  bushy  dendrites  directed  outward  and 
slender  axons  directed  inward.  These  axons  are  myelinated 
and  constitute  the  chief  efferent  pathway  from  the  cortex; 
they  do  not,  however,  leave  the  cerebellum,  but  end  in  the  deep 
gray  nuclei  (chiefly  the  dentate  nuclei),  from  which  other 
neurons  carry  the  impulses  out  of  the  cerebellum.  The 
dendrites  of  the  Purkinje  cells  are  widely  expanded  trans- 
versely to  the  length  of  the  folium,  but  are  very  narrow  in  the 
opposite  direction;  thus  each  cell  comes  into  contact  with 
the  largest  possible  number  of  axons  of  the  granule  cells  which 
run  lengthwise  of  the  folium.  The  outermost  or  molecular 
layer  contains  the  dendrites  of  the  Purkinje  cells,  termini  of 
the  axons  of  the  granule  cells  and  of  other  fibers,  and  a  small 
number  of  neurons  with  short  axons,  among  which  are  the 
basket  cells  illustrated  in  Figs.  16  and  89,  b. 

Afferent  fibers  terminate  in  the  cerebellar  cortex  in  two 
ways.  They  may  pass  directly  out  to  the  molecular  layer  as 
ascending  or  climbing  fibers,  where  they  end  in  very  intimate 
relation  with  the  dendrites  of  the  Purkinje  cells  (Figs.  15  and 


214  INTRODUCTION  TO  NEUROLOGY 

89,  n),  or  they  may  end  as  moss  fibers  (Fig.  89,  h)  among 
the  cells  of  the  granule  layer.  Here  the  granules  take  up  the 
nervous  impulses  and  deliver  them  to  the  dendrites  of  the 
Purkinje  cells.  Ramon  y  Cajal  is  of  the  opinion  that  the 
moss  fibers  are  the  terminals  of  the  afferent  fibers  of  the  inferior 
cerebellar  peduncle,  and  that  the  ascending  fibers  are  the 
terminals  of  the  fibers  from  the  middle  peduncle  (brachium 
pontis) . 

Since  each  fiber  from  the  inferior  peduncle  branches  exten- 
sively and  reaches  many  granule  cells  in  widely  separated  parts 
of  the  cerebellum,  and  since  the  axon  of  each  granule  cell 
reaches  the  dendrites  of  a  very  large  number  of  Purkinje  cells, 
a  single  incoming  nervous  impulse  may  excite  a  very  large 
number  of  Purkinje  cells,  and  thus  its  physiological  effect  may 
be  greatly  enhanced.  The  same  result  is  also  secured  by  the 
action  of  the  basket  cells  (Fig.  89,  h)  and  other  forms  of  neurons 
with  short  axons  within  the  cortex  (Fig.  89,  e,  J) ,  each  of  which 
may  discharge  powerful  impulses  directly  upon  several 
Purkinje  cells.  The  axons  of  the  Purkinje  cells  themselves 
also  give  off  collateral  fibers  into  the  granular  layer,  whose 
neurons  discharge  back  into  the  Purkinje  cells  again.  In  all 
of  these  ways  provision  is  made  for  the  diffusion,  summation, 
and  reinforcement  of  stimuli  during  the  process  of  their 
transmission  through  the  cerebellar  cortex,  and  also  for  pro- 
longation of  motor  reactions  which  would  otherwise  soon 
subside,  and  for  the  maintenance  of  muscular  tone. 

This  type  of  reaction  has  been  termed  "avalanche  con- 
duction" (see  p.  107),  and  its  mechanism  here  is  similar  to 
that  found  in  the  olfactory  bulb  (p.  242),  but  much  more 
complex.  It  is  probable  that  the  reciprocal  relation  between 
the  cerebellum  and  the  cerebral  cortex  is  of  a  similar  sort,  all 
cortical  activities  exciting  also  the  cerebellum  and  drawing 
therefrom  additional  nervous  energy  as  needed  to  maintain  the 
tone  of  the  reacting  mechanism;  and  voluntary  movements 
excited  by  the  cortico-spinal  or  pyramidal  tract  from  the  cere- 
bral cortex  (see  p.  317)  are  under  especially  direct  pro- 
prioceptive control  from  this  source. 

The  relationships  of  the  centers  of  the  brain  stem,  the 
cerebral  cortex,  and  the  cerebellum  may  be  illustrated  some- 


thp:  vestibular  apparatus  and  cerebellum       215 

what  crudely  by  the  analogy  of  the  three  chief  departments  of 
the  national  government.  The  reflex  centers  of  the  brain  stem 
correspond  to  the  legislative  branch  of  government,  determin- 
ing in  advance  by  virtue  of  their  innate  structure  what  actions 
may  appropriately  be  performed  in  each  particular  type  of 
frequently  recurring  situation.  The  cerebral  cortex  is  a  sort 
of  glorified  judicial  branch  of  government,  interpreting  the 
decrees  of  the  legislative  centers,  integrating  the  behavior 
by  combining  its  elements  into  cooperating  systems  in  view 
of  all  the  factors  of  present  and  past  experience,  and  with 
extensive  powers  of  veto  over  inappropriate  reactions  which 
may  have  been  inaugurated  by  the  lower  centers.  The 
cerebellum  is  the  great  administrative  office  which  attends 
to  the  details  of  the  proper  execution  of  the  acts  which  have 
been  previously  determined  upon  and  initiated  in  the  other 
departments  of  government. 

Summary. — The  vestibular  apparatus  and  the  cerebellum 
are  genetically  and  physiologically  very  closely  related.  The 
semicircular  canals  are  the  most  highly  differentiated  pro- 
prioceptive end-organs,  serving  chiefly  the  functions  of 
equilibration  and  the  maintenance  of  muscular  tone.  These 
reactions  are,  for  the  most  part,  unconsciously  performed 
and  there  is  no  important  cortical  path  from  the  vestibular 
nuclei.  These  nuclei  effect  reflex  connections  with  the  motor 
centers  of  the  spinal  cord  and  medulla  oblongata,  especially 
the  eye-muscle  nuclei,  and  with  the  cerebellum. 

The  cerebellum  has  been  developed  out  of  the  primary 
vestibular  area  for  the  more  perfect  coordination  and  integra- 
tion of  the  somatic  motor  reactions  and  for  strengthening 
these  reactions.  It  receives  afferent  fibers  from  all  somatic 
sensory  centers,  and  in  mammals  it  is  also  very  intimately 
connected  with  the  cerebral  cortex,  these  two  higher  centers 
appearing  always  to  act  conjointly.  The  cerebellum  dis- 
charges into  all  of  the  somatic  motor  centers  and  assists  in 
preserving  the  proper  balance  of  muscular  contraction  and 
in  the  maintenance  of  muscular  tone. 

Literature 

For  llic  orifiiuai  soureos  of  the  data  presented  in  this  and  the  preced- 
ing chapters  see  the  bihhographies  appended  to  Chapters  \'II,  VIII,  IX, 
and  X.     On  the  eerebcdhini  se(>  further: 


216  INTRODUCTION  TO  NEUROLOGY 

Andre-Thomas  and  Durupt,  A.  1914.  Localisations  cerebelleuses, 
Paris. 

Barany,  R.  1912.  Lokalization  in  cler  Rinde  der  Kleinhirnhemi- 
spharen  des  Menschen,  Wiener  klin.  Wochenschr.,  Jahrg.  xxv,  No.  52, 
pp.  2033-2038. 

BiANCHi,  A.  1903.  Sulle  vie  di  connessione  del  cervelletto,  Arch.di 
Anat.  e  EmbrioL,  vol.  ii. 

Black,  D.  1916.  Cerebellar  Localization  in  the  Light  of  Recent 
Research,  Jour.  Lab.  and  Clin.  Med.,  vol.  i,  No.  7. 

BoLK,  L.     1906.     Das  Cerebellum  der  Satigethiere.  Jena. 

Bruce,  A.  N.  1910.  The  Tract  of  Gowers,  Quart.  Jour.  Exp. 
Physiol.,  vol.  iii,  pp.  391-407. 

Ferrier,  D.,  and  Turner,  W.  A.  1895.  A  Record  of  Experiments 
Illustrative  of  the  Symptomatology  and  Degenerations  Following 
Lesions  of  the  Cerebellum,  Phil.  Trans.  Roy.  Soc.  London  for  1894,  vol. 
clxxxv  B,  pp.  75.5-761. 

Gehuchten,  a.  Van.  1904.  Le  corps  restiforme  et  les  connexions 
bulbo-cerebelleuses,  Le  Nevraxe,  vol.  vi. 

— .  1905.  Les  pedoncules  cerebelleuses  superieurs,  Le  Nevraxe,  vol. 
vii. 

Goldstein,  K.  1910.  Ueber  die  aufsteigende  Degeneration  und 
Querschnittsunterbrechung  des  Rlickenmarks  (Tractus  spino-cerebellaris 
posterior,  Tractus  spino-olivaris,  Tractus  spino-thalamicus),  Neurol. 
Centralblatt,  No.  17. 

Herrick,  C.  Jud.son.  1914.  The  Cerebellum  of  Necturus  and  Other 
Urodele  Amphibia,  Jour.  Comp.  Neur.,  vol.  xxiv,  pp.  1-29. 

Herrick,  C.  L.  1891.  Illustrations  of  the  Architectonic  of  the  Cere- 
bellum, Jour.  Comp.  Neur.,  vol.  i,  pp.  6-14. 

Lewandowsky,  M.  1907.  Die  Funktionen  des  zeiitralen  Nervensys- 
tems,  Jena. 

Luciani,  L.     1893.     Das  Kleinhirn,  Leipzig. 

— •.     1915.     Human  Phj^siology,  New  York. 

Russell,  J.  S.  Risien.  189,5.  Experimental  Researches  into  the 
Functions  of  the  Cerebellum,  Phil.  Trans.  Rov.  Soc.  London,  vol.  clxxxv 
B,  pp.  819-861. 

Van  Rynberk,  G.  1908,  1912.  Das  Lokalizationsproblem  im  Klein- 
hirn, Ergebnisse  der  Phvsiol.,  Bd.  vii,  1908,  pp.  653-698.  and  Bd.  xii, 
1912,  pp.  533-563. 

ScHAPER,  A.  1894.  Die  morphologische  und  histologische  Entwick- 
elung  des  Kleinhirns  der  Teleostier,  Morph.  Jahrb.,  Bd.  xxi. 

Sherrington,  C.  S.  1909.  On  Plastic  Tonus  and  Proprioceptive 
Reflexes,  Quart.  Jour.  Exp.  Physiol.,  vol.  ii,  p.  109. 

Smith,  G.  Elliot.  1903.  Further  Observations  on  the  Natural 
Mode  of  Subdivision  of  the  Mammalian  Cerebellum,  Anat.  Anz.,  Bd. 
xxiii,  pp.  368-384. 

Strong,  O.  S.  1915.  A  Case  of  Unilateral  Cerebellar  Agenesia, 
Jour.  Comp.  Neur.,  vol.  xxv,  pp.  361-391. 

Wilson,  J.  Gordon,  and  Pike,  F.  H.  1912.  The  Effects  of  Stimula- 
tion and  Extirpation  of  the  Labyrinth  of  the  Ear,  and  Their  Relation  to 
the  Motor  System,  Phil.  Trans.  Roy.  Soc.  London,  vol.  cciii  B,  pp. 
127-160. 


CHAPTER  XIII 
THE  AUDITORY  APPARATUS 

The  human  organ  of  hearing  consists  of  the  external  ear, 
bounded  within  by  the  drum  membrane  (tj-mpanic  membrane, 
membrana  tympani);  the  middle  ear,  a  cavity  filled  with  air 
which  communicates  with  the  pharynx  through  the  auditory 


Tympanic  cavity,  with  cliain  of  ossicles 
Semicircular  duct 
Utricle 
Ductus  endolymphaticus 
Saccule 
Ductus  cochleans 


Auditory  tube 

Membrana  tympani 

Recessus  epitympanicus 

External  acoustic  meatus 


Fig.   VK). — DiagraiiiiiKitic    view    of    the    parts    of    the    hmnaii    ear.      (From 
{ ■uiiuiiigham's  Anatomy.) 

or  Eustachian  tube  and  contains  the  auditory  ossicles;  and  the 
internal  ear,  a  complex  bony  chamber,  the  bony  labyrintii, 
within  which  is  the  membranous  labj-rinth  containing  the 
specific   receptors    or   sensory    surfaces    of   the   internal   ear 

217 


218 


INTRODUCTION    TO    NEUROLOGY 


(Fig.  90).  The  tympanic  membrane  receives  tiie  air  waves 
which  form  the  physical  stimuh  of  sound  (pp.  75  and  92). 
These  vibrations  are  then  transmitted  (and  at  the  same  time 
intensified  about  thirty-fold)  by  the  auditory  ossicles  of  the 
middle  ear  to  the  liquid  within  the  bony  labyrinth. 

The  membranous  labyrinth  is  of  approximately  the  same 
shape  as  the  bony  labyrinth,  but  smaller,  so  that  there  is  a 
space  between  the  membranous  labyrinth  and  the  enclosing 
bony  wall.  This  space  is  filled  with  liquid,  the  perilymph, 
and  the  inembranous  labyrinth  is  also  filled  with  liquid,  the 
endolymph.  In  Fig.  90  the  perilymphatic  space  is  printed 
in  black  and  the  endolymphatic  space  in  white.  The  parts 
of  the  membranous  labyrinth  are  shown  diagrammatically 
in  Fig.  91. 

Recessus  utriculi  * 

Saccule 


Ampulla  of  superior  semi- 
circular duct 
Ampulla  of  lateral  duct 


Ductus  cochlearis-^— 
Ductus  reuniens 
Ductus  endolymphaticus 


Ampulla  of  posterior  duct 


Crus  commune 

Ductus  utriculosaccularia 

Sinus  inferior 


Saccua  endolymphaticus  - 

Fig.   9i. — Diagrammatic    representation    of    the   parts    of    the    membranous 
labyrinth.      (From  Cunningham's  Anatomy.) 

The  membranous  labyrinth  is  a  closed  sac  which  has  four 
chief  parts:  (1)  the  utricle  (recessus  utriculi),  with  a  patch  of 
sensory  epithelium,  the  macula  utriculi;  (2)  the  three  semi- 
circular canals  (ductus  semicirculares) ,  each  of  which  com- 
municates at  both  ends  with  the  utricle  and  has  at  one  end  a 
dilation  (ampulla)  containing  a  patch  of  sensory  epithelium, 
the  crista;  (3)  the  saccule  (sacculus)  connected  by  a  narrow 
ductus  utriculosaccularis  with  the  utricle  and  containing  a 
patch  of  sensory  epithelium,  the  macula  sacculi;  (4)  the 
ductus  cochlearis,  which  communicates  by  a  narrow  ductus 
reuniens  with  the  saccule  and  is  spirally  wound  to  fit  the 
bony  cochlea,  which  is  shaped  like  a  snail  shell.  The  ductus 
cochlearis    (old   name,    scala   media)    is   triangular   in  cross- 


THE    AUDITORY    APl'AUATUS 


21<) 


section  (Fig.  92)  and  contains  the  sppcific  auditory  iec'(![)tivc 
epithelium  in  tlie  spiral  organ,  or  organ  of  Corti. 

The  org.'))!  of  Corti  is  a  very  highly  differf-iitiaicfl  sensory  epithelium 
which  rests  upon  a,  firm  basilar  inembrane  (Fig.  02,  iiiombrana  l')asilaris). 
Many  details  of  the  structure  of  this  organ  and  the  wliole  question  of  the 
mode  of  its  functioning  are  still  controverted.  Figure  93  has  been  drawn 
for  this  work  by  Dr.  O.  Van  der  Stricht  to  illustrate  his  observations. 

The  sensory  epithelium  consists  of  non-sensory  supporting  cells  of 
several  sorts  and  four  or  five  rows  of  specific  sensory  cells,  the  auditory 
hair  cells.  The  supporting  cells  assume  various  forms  in  different  parts 
of  the  epithelium,  and  two  rows  of  these  cells  are  specially  modified  to 
form  the  firm  inner  and  outer  pillars  which  incline  toward  each  other  to 
enclose  the  tunnel  of  Corti.     The  sensory"  cells  are  arranged  in  one  row  of 


Membrana  yestibula; 


Inner  hair  cell 

Outer  hair  cells 

Membrana  basilaris 

SCALA  TYMPANl 

Fig.  92. — Section  across  the  ductus  cochlearis  (scala  media)  t(j  illustrate  the 
relations  of  the  spiral  organ  (organ  of  Corti).      (After  Retzius.) 

inner  hair  cells  and  three  or  four  rows  of  outer  hair  cells  on  opposite  sides 
of  the  tunnel  of  Corti.  These  hair  cells  extend  only  part  way  through  the 
thickness  of  the  epithelium  and  the  supporting  cells  below  and  between 
the  outer  hair  cells  are  known  as  the  cells  of  Deiters.  Within  eachof 
these  cells  is  a  stiff  axial  filament  which  expands  to  form  a  chalice-like 
support  under  the  base  of  a  hair  cell. 

The  fibers  of  the  cochlear  nerve  pass  outward  from  the  axis  of  the 
spiral  of  the  cochlea,  then  upward  to  traverse  the  tunnel  of  Corti.  Here 
some  turn  to  form  a  longitudinal  trunk  within  the  tunnel  (Fig.  9.3,  N). 
Fibers  leave  this  trunk  to  cross  the  tunnel  transversely  and  end  in  rela- 
tion with  the  outer  hair  cells.  The  termini  of  the  fibers  of  the  cochlear 
nerve  arborize  around  the  bases  of  the  hair  cells  in  the  same  way  that 
fibers  of  the  vestibular  nerve  are  related  to  the  hair  cells  of  the  cristiipof 
the  semicircular  canals  (Fig.  32,  p.  94). 


220  INTRODUCTION  TO  NEUROLOGY 

The  tectorial  membrane  (membrana  tectoria)  is  a  delicate  gelatinous 
mass  resting  upon  the  organ  of  Corti  and  intimately  connected  with  the 
liairs  of  the  hair  cells.  Its  shape  and  properties  have  been  carefully 
studied  by  Hardesty. 

The  development  of  the  tectorial  membrane  has  been  restudied  by 
Prentiss  and  Hardesty  and  still  more  recently  by  Van  der  Stricht.  It 
first  appears  as  a  thin  cuticular  plate  developed  over  the  free  ends  of  the 
columnar  cells  which  form  the  inner  or  axial  part  of  the  epithehum  on  the 
basilar  membrane.  In  the  adult  ear  it  retains  its  attachment  to  the  lim- 
bus  of  the  spiral  lamina  along  the  axial  border  of  this  epithelium,  but 
becomes  free  from  the  cells  which  form  the  hning  of  the  spiral  sulcus. 
Prentiss  describes  the  membrane  as  growing  in  thickness  by  the  secretion  of 
a  cuticulum  formed  between  the  ends  of  the  epithelial  cells,  thus  giving 
to  the  mature  membrane  a  chambered  or  honey-comb  structure.  _ 

Van  der  Stricht  confirms  Prentiss'  observation  that  the  tectorial  mem- 
brane arises  from  the  epithelium  lining  the  limbus  of  the  spiral  lamina,  the 
future  spiral  sulcus  and  the  organ  of  Corti,  and  he  adds  further  details  of 
the  development  and  adult  structure  of  this  region.  In  early  embryos  the 
intercellular  substance  becomes  condensed  between  the  apices  of  the 
epithelial  cells  and  forms  the  "terminal  bars"  which  close  the  intercellu- 
lar spaces.  These  bars  take  a  large  part  in  the  development  of  the  tec- 
torial membrane  and  the  fenestrated  membrana  reticularis  of  the  organ  of 
Corti.  The  tectorial  membrane  is  made  up  of  cylinders  or  prisms,  the 
denser  part  of  which  (the  walls)  arises  from  the  terminal  bars  and  the 
more  fluid  part  (their  content)  arises  from  the  cytoplasmic  apices  of  the 
subjacent  epithelial  cells.  The  membrana  reticularis  is  represented  by 
the  primitive  terminal  bars,  which  at  the  level  of  the  organ  of  Corti  and 
after  the  development  of  the  tectorial  membrane  become  very  thick, 
mainly  around  the  apices  of  the  hair  cells,  and  give  rise  to  the  fenestrated 
membrane  with  two  kinds  of  openings:  rounded  apertures  through  which 
project  the  hairs  of  the  auditory  hair  cells  and  others  of  various  shape  and 
size  which  are  closed  by  the  apices  of  the  supporting  cells. 

Regarding  the  functions  of  these  parts,  our  present  knowledge  of  the 
histological  organization  of  the  basilar  membrane  shows  that  it  is  struc- 
turally incapable  of  serving  the  function  of  tone  analysis  in  the  way  pos- 
tulated by  Helmholtz'  theory.  The  tectorial  membrane  is  probably  the 
medium  through  which  sound  waves  are  transmitted  to  the  auditory 
receptors,  viz.,  the  hair  cells.  Shambaugh  and  Prentiss  are  of  the  opinion 
that  the  hairs  of  the  hair  cells  are  firmly  attached  to  the  tectorial  mem- 
brane (Fig.  94),  which  has  a  semi-gelatinous  texture  and  is  capable  of  tak- 
ing up  sympathetically  the  vibrations  of  the  endolymph  withinwhich  it 
floats.  According  to  this  theory  the  tectorial  membrane  functions  as  a 
physical  resonator,  effecting  tone  analysis  by  responding  in  its  various 
parts  to  tones  of  different  pitch,  depending  on  the  size  of  the  membrane. 
Tones  of  higher  pitch  would  be  taken  up  by  the  hair  cells  located  near  the 
beginning  of  the  basal  coil,  those  of  lower  pitch  by  the  cells  near  the  apex 
of  the  cochlea,  where  the  tectorial  membrane  attains  its  maximum  size. 

Hardesty  has  constructed  a  large  mechanical  model  to  illustrate  the 
probable  working  of  the  spiral  organ  and  especially  of  the  tectorial  mem- 
brane. His  artificial  tectorial  membrane  can  be  excited  to  vibration  by 
sound  waves  of  different  pitch  and  is  capable  of  effecting  a  limited  degree 
of  tone  analysis.  Although  the  model  gave  some  results  which  suggest 
the  possibiHty  that  the  tectorial  membrane  may  act  as  a  physical  resona- 


THE    AUDITORY    APPARATUS 


221 


T  •    1         f  17       •      /  Zona  papillaris 

Limbus  of  spiral  lamina       ^^na  dentata 


Tectorial  membrane 

Internal  spiral  sulcus 

Stripe  of  Hensen 

Inner  hair  cells 

Outer  hair  rcllr 


Cells  of 
Hensen 


Cells  of    Basilar  Quter 

Claudius  membrane  pillar 

Cells  of  Deiters  Tunnel   Inner 

of  Corti  pillar 


Cochlear  nerve 


E.  S.  C. 


Fig.  93. — Diagrammatic  cross- section  of  the  spiral  organ  (organ  of  Corti) 
of  the  adult  rat.  The  teeth  of  Huschke  are  represented  as  if  cut  transversely 
in  a  slightly  different  plane  from  the  remainder  of  the  section.  The  innerva- 
tion is  very  diagrammatically  indicated  after  the  researches  of  Held  (1902). 
Drawn  by  Dr.  O.  Van  dcr  Stricht  (for  further  details  see  his  paper  (1918) 
cited  in  the  appended  bibliography).  A.  Spiral  vessel;  E.S.C.,  epithelium 
of  spiral  fuIcus;  A',  longitudinal  nerve  of  tunnel  of  Corti. 


n.cocn^ 


Fig.  9-4. — Section  through  the  apical  turn  of  the  cochlea  of  the  pig  at 
about  full  term,  showing  outer  auditory  hairs  embedded  in  the  membrana 
tectoria:  ip.-s.sp..  epithelium  of  spiral  sulcus;  i.li.c.  inner  hair  cells;  i.pil.. 
inner  pillar;  m.has.,  basilar  membrane;  m.tect.,  membrana  tectoria;  lab. 
vest.,  lahitmi  vestibulare;  n.  cock.,  cochlear  nerve;  o.h.c,  outer  hair  cell;  s.sp., 
sulcus  spiralis;  st.H..  stripe  of  Hensen.     (After  C.  W.  Prentiss.) 


222  INTRODUCTION    TO    NEUROLOGY 

tor  in  effecting  tone  analysis  as  suggested  by  Shambaugh,  the  entire  arti- 
ficial tectorial  membrane  is  thrown  into  vibration  by  sounds  of  low  pitch, 
and  Hardesty  is  of  the  opinion  that  there  is  no  apparatus  in  the  internal 
ear  capalDle  of  acting  as  a  physical  resonator.  The  problem  of  the  mode 
function  of  the  spiral  organ  is  as  yet  unsolved. 

In  fishes  the  organs  of  the  internal  ear  are  intimately  associated  with  an 
extensive  series  of  subcutaneous  canals  containing  numerous  sense  organs 
and  with  naked  cutaneous  sense  organs  of  the  same  type,  the  entire  com- 
plex forming  the  system  of  lateral  line  sense  organs  (see  p.  120  and  Fig. 
95).  The  nerves  which  in  fishes  supply  the  lateral  line  sense  organs  (later- 
alis roots  of  the  VII  and  X  cranial  nerves)  and  the  organs  of  the  internal 
ear  (VIII  nerve)  are  intimately  associated  and  terminate  together  in  the 
acoustico-lateral  area  of  the  medulla  oblongata  (Figs.  43  and  44,  pp.  119, 
120),  and  all  of  these  end-organs  have  the  same  type  of  structure  as  those 
of  the  human  internal  ear  (Fig.  32,  p.  94). 

The  internal  ears  of  fishes  are  essentially  similar  to  those  of  man  save 
that  they  lack  the  cochlea  and  the  organ  of  Corti.  They  possess  a  small 
sense  organ  in  the  saccule,  the  lagena,  supplied  by  a  special  branch  of  the 
VIII  nerve  (Fig.  95,  RL),  from  which  the  cochlea  of  higher  vertebrates  has 
been  developed.  The  researches  of  Parker  have  shown  that  fishes  hear, 
though  there  is  no  evidence  that  they  possess  the  power  of  tone  analysis, 
and  the  sense  organs  of  the  saccule  are  the  essential  receptors  for  sound 
waves.  The  sense  organs  of  the  lateral  line  system  are  said  by  Parker  to 
be  sensitive  to  water  vibrations  of  slower  frequency  than  the  sound  waves 
to  which  the  ear  responds,  while  Hof er  is  of  the  opinion  that  these  organs 
are  stimulated  only  by  streaming  movements  of  the  water  in  which  the 
animals  live.  ProlDably  the  lateral  line  organs  also  participate  in  the 
equilibratory  reactions  of  the  fish.  i 

Though  our  knowledge  of  the  functions  of  the  various  parts  of  the 
acoustico-lateral  system  of  fishes  is  still  very  imperfect,  it  is  evident  that 
all  of  these  organs  are  both  structurally  and  physiologically  of  common 
type,  and  it  is  probable  that  they  have  had  a  common  evolutionary  origin 
from  a  more  generalized  form  of  cutaneous  tactile  organ.  This  is  the 
explanation  of  the  intimate  association  in  the  human  ear  of  sense  organs 
of  so  diverse  functions  as  the  cochlea  for  hearing  and  the  semicircular 
canals  for  equilibration,  the  former  being  an  exteroceptor  whose  reactions 
may  be  vividly  conscious,  and  the  latter  being  a  proprioceptor  whose 
reactions  are  almost  entirely  unconsciously  performed.  For  further  con- 
sideration of  the  semicircular  canals  and  their  central  connections  see 
p.  201. 

In  the  human  body  the  cochlear  and  vestibular  nerves  are 
very  intimately  associated,  but  the  embryological  studies  of 
Streeter  and  others  have  made  it  plain  that  these  two  nerves  are 
really  more  distinct  than  was  formerly  supposed.  The  periph- 
eral receptors  of  the  cochlea  and  semicircular  canals  are 
obviously  as  dissimilar  as  are  theii'  functions,  but  the  functional 
significance  of  the  sensory  organs  of  the  utricle  and  saccule  is 
more  uncertain.  The  fact  that  fishes  undoubtedly  hear,  not- 
withstanding their  lack  of  cochlea  or  any  other  receptors  mor^ 


TTTE    AirDlTOltY    APPARATtrS 


223 


complex  than  \hv  sciisoiy  spots  in  the  saccuh',  demonsl rates 
the  relatively  late  phylogenetic  oiigin  of  the  cochlear  system 


Fig.  95. — Diagram  of  the  acoustico-lateral  system  of  nerves  with  their 
peripheral  end-organs,  as  seen  from  the  right  side,  in  a  fish,  the  common 
silver-sides,  Menidia  (X  9).  The  relations  here  figured  were  reconstructed 
from  serial  sections  by  projection  upon  the  sagittal  plane.  For  the  relations 
between  the  acoustico-lateral  nerves  and  the  other  systems  of  nerves  in  this 
fish,  see  the  more  detailed  chart  from  which  this  was  drawn  off,  in  the  Journal 
of  Comparative  Neurology,  vol.  ix,  1899,  plate  15;  cf.  also  Fig.  65,  p.  163, 
of  this  book.  The  dotted  outline  repiesents  the  position  of  the  brain,  the 
lateral  line  canals  are  shaded  with  cross-hatching,  the  internal  ear  is  stippled, 
and  the  nerves  are  drawn  in  black.  The  organs  of  the  lateral  line  system 
are  drawn  as  black  disks  when  naked  on  the  surface  of  the  skin,  and  as  black 
circles  when  lying  in  the  canals.  A'^.4,  anterior  nasal  aperture;  N^AP. 
posterior  nasal  aperture;  A'  OL,  olfactory  nerve;  A'  OPT,  optic  nerve;  RAA. 
nerve  of  superior  ampulla;  RAE,  nerve  of  lateral  ampulla;  RAP,  nerve  of 
inferior  ampulla;  R  BUC,  ramus  buccalis  of  facial  nerve;  RL,  nerve  of  the 
lagena  (rudimentary  spiral  organ);  R  LAT.  ramus  lateralis  of  the  vagus; 
R  OS,  ramus  ophthalmicus  superficialis  of  the  facial  nerve;  R  MAA^  EX, 
ramus  mandibularis  externus  of  the  facial  nerve;  7?  SAC,  nerve  of  thesaccu- 
lus;  RU,  nerve  of  the  utriculus;  T,  acoustico-lateral  area.  (After  Herrick, 
from  Wood's  Reference  Handbook  of  the  Medical  Sciences,  Article,  "Ear.") 

from  the  vestibular,  and  has  suggested  to  some  phj-siologists 
that  even  in  man  these  two  systems  are  not  wholly  distinct, 
and  that  the  sense  organs  in  the  saccule  may  also  function  as 


224 


INTRODUCTION    TO    NEUROLOGY 


a  sound  receptor.     It  is  clear,  however,  that  tone  analysis  is 
effected  only  in  the  cochlea. 

The  central  connections  of  the  cochlear  and  vestibular  nerves 
are  fundamentally  different.     The  vestibular  nerve  terminates 


Nucleus  of  lateral  lemniscus 
Medial  longitudinal  fasciculus  --- 
Lateral  lenmiscu: 


Peduncle  of  superior  olive 


^Inferior  quadrigeminate  body 


Nucleus  of  trochlear  nerve 


Nucleus  fastigii 

Nucleus  emboliformis 


'  Dentate  nucleus 


^  Lateral  nucleus  of 
■  '  '  vestibular  nerve 
Restlform  body 
^Dorsal  nucleus  of 

cochlear  nerve 
^Ventral  nucleus  ot 

cochlear  nerve 
.•Cochlear  nerve 


Vestibular  neive 


Superior  olivary  nucleus 


Trapezoid  body 
Fig.  96. — Diagram  of  the  auditory  and  vestibular  connections.  Com- 
pare Kgs.  71,  77,  and  86.  The  fibers  of  the  cochlear  nerve  enter  the  ven- 
tral and  dorsal  cochlear  nuclei  (the  latter  being  termed  the  tuberculum 
acusticum)  at  the  lateral  border  of  the  medulla  oblongata.  The  auditory 
path  now  divides,  one  tract,  the  trapezoid  body,  passing  ventrally  through 
the  pons  to  enter  the  lateral  lemniscus  of  the  opposite  side,  and  the  other 
passing  dorsally  through  the  acoustic  medullary  striae  (striae  medullares 
acustici)  across  the  floor  of  the  fourth  ventricle  and  also  entering  the  lateral 
lemniscus.  These  fibers  may  be  interrupted  by  synapses  in  the  superior 
olives,  the  nucleus  of  the  lateral  lemniscus  or  the  inferior  colliculus  (inferior 
quadrigeminate  body)  before  they  reach  the  medial  geniculate  body  of  the 
thalamus,  or  they  may  pass  by  these  nuclei  without  connecting  with  them. 
The  fibers  shown  in  the  diagram  as  passing  from  the  inferior  quadrigeminate 
body  to  the  temporal  lobe  of  the  cerebral  cortex  are  probably  interrupted  by 
a  synapse  in  the  medial  geniculate  body.     (From  Morris'  Anatomy.) 


in  reflex  centers  of  the  medulla  oblongata  and  cerebellum  (p. 
203)  with  no  important  cortical  connections,  while  the  cochlear 


^.  THE    AUDITORY    APPARATUS  225 

nerve  has,  in  addition  .to  the  important  reflex  connections  in  tlie 
oblongata  and  midbrain,  the  much  stronger  ascending  pathway 
of  the  lateral  lemniscus  directly  to  the  medial  geniculate  body 
of  the  thalamus,  and  thence  to  the  temporal  lobe  of  the  cerebral 
cortex  (see  p.  171  and  Figs.  75,  77,  80,  96).  Some  of  the  fibers 
of  the  lateral  lemniscus  are  interrupted  in  the  inferior  colliculus, 
which  is  an  important  auditory  reflex  center. 

Reflex  responses  to  auditory  stimuli  may  be  effected  by 
collateral  connections  made  at  various  points  along  the  course 
of  the  main  cortical  path  in  the  lateral  lemniscus.  Some  of 
these  points  of  synapse  are,  the  superior  olives,  nuclei  of  the 
trapezoid  body,  nuclei  of  the  lateral  lemniscus,  and  inferior 
colliculus  (Fig.  96).  Most  of  these  collateral  connections  are 
relatively  short  tracts  connecting  directl}^  with  the  adjacent 
motor  nuclei  of  the  midbrain  and  medulla  oblongata.  Spinal 
reflexes  are  made  by  the  tecto-spinal  tract  from  the  inferior  col- 
liculus, part  of  these  fibers  first  decussating  in  the  dorsal 
tegmental  decussation  of  the  midbrain  (Figs.  59,  73,  75). 

Summary. — The  human  ear  has  three  parts:  (1)  the  external 
ear,  for  receiving  sound  waves  from  the  air;  (2)  the  middle  ear, 
for  intensifying  the  vibrations  and  transmitting  them  to  (3)  the 
internal  ear,  which  is  filled  with  liquid  and  contains  sense  or- 
gans of  uncertain  function  in  the  utricle  and  saccule,  sense 
organs  for  equilibration  in  the  semicircular  canals,  and  the 
spiral  organ  (organ  of  Corti)  in  the  cochlea  for  tone  analysis. 
The  spiral  organ  is  a  complicated  epithelial  structure  resting 
on  a  basilar  membrane  and  consisting  of  supporting  cells 
of  diverse  kinds,  the  hair  cells  (which  are  the  specific  receptors 
and  receive  the  endings  of  the  fibers  of  the  cochlear  nerve), 
and  the  tectorial  membrane.  Shambaugh  is  of  the  opinion 
that  the  tectorial  membrane  is  capable  of  responding  in  its 
various  parts  to  different  vibration  frequencies,  and  that  the 
hair  cells  are  stimulated  through  their  hairs  which  are  attached 
to  the  tectorial  membrane. 

In  fishes  the  organ  of  hearing  is  much  simpler  than  in  man, 
the  semicircular  canals  are,  however,  similar,  and  there  is,  in 
addition,  an  elaborate  sj^stem  of  lateral  line  sense  organs  whose 
functions  seem  to  be  intermediate  between  the  tactile  and  audi- 
tory organs.     It  is  probable  that  these  three  systems  of  sense 

15 


226  INTRODUCTION  TO  NEUROLOGY 

organs  were  derived  phylogenetically  from  some  more  gener- 
alized form  of  cutaneous  tactile  organ.  This  accounts  for  the 
intimate  association  in  the  human  ear  of  organs  of  so  diverse 
functions  as  the  semicircular  canals  and  the  cochlea. 

The  central  connections  of  the  vestibular  and  cochlear  nerves 
are  very  different,  the  former  effecting  chiefly  reflex  connec- 
tions for  equilibration  in  the  medulla  oblongata  and  cerebel- 
lum, and  the  latter  both  reflex  connections  in  the  brain  stem 
and  cortical  connections  through  the  lateral  lemniscus,  medial 
geniculate  body  of  the  thalamus  and  auditory  radiations,  for 
conscious  sensations  of  hearing. 

Literature 

EwALD,  J.  R.  1892.  Physiologische  Untersuchungen  iiber  das  End- 
organ  des  Nervus  octavus,  Wiesbaden,  J.  F.  Bergmann. 

Hardesty,  I.  1908.  On  the  Nature  of  the  Tectorial  Membrane  and 
Its  Probable  Role  in  the  Anatomy  of  Hearing,  Amer.  Jour.  Anat.,  vol.  viii. 

— ,  1915.  On  the  Proportions,  Development,  and  Attachment  of  the 
Tectorial  Membrane,  Amer.  Jour.  Anat.,  vol.  xviii. 

— .  1915a.  A  Model  to  Illustrate  the  Probable  Action  of  the  Tec- 
torial Membrane,  Am.  Jour.  Anat.,  vol.  xviii,  pp.  471-514. 

Held,  H.  1902.  Untersuchungen  iiber  den  feineren  Bau  des  Ohr- 
labyrinthes  der  Wirbeltiere.  I.  Abh.  Icon.  Sachs.  Gosells.  Wissen.,  Leip- 
zig, Bd.  40,  pp.  1-74. 

VON  Helmholtz,  H.  L.  T.  1896.  Die  Lehre  von  den  Tonempfindun- 
gen,  Ausgabe  5,  Braunschweig. 

HoFER,  N.  1908.  Studien  iiber  die  Hautsinnesorgane  der  Fische, 
Berichte  kgl.  Baj^erischen  Biologischen  Versuchsstation  in  Miinehen,  Bd. 
1,  p.  115. 

Kappers,  C.  U.  Ariens.  Kurze  Skizze  der  Phylogenetischen  Ent- 
wicklung  der  Oktavus  und  Lateralisbahnen  mit  Beriicksichtigung  der 
neuesten  Ergebnisse,  Zentralbl.  f.  Physiol.,  Bd.  23,  1909. 

Parker,  G.  H.  1903.  Hearing  and  Allied  Senses  in  Fishes,  U.  S. 
Fish  Commission  Bulletin  for  1902,  Washington. 

— .  1903.  The  Sense  of  Hearing  in  Fishes,  Amer.  Naturalist,  vol. 
xxxvii. 

— .  1905.  The  Function  of  the  Lateral  Line  Organs  in  Fishes,  Bull,  of 
the  Bureau  of  Fisheries  for  1904,  Washington. 

Prentiss,  C.  W.  1913.  On  the  Development  of  the  Membrana  Tec- 
toria  with  Reference  to  Its  Structure  and  Attachments,  Amer.  Jour. 
Anat.,  vol.  xiv,  No.  4. 

Retzius,  G.     1884.     Das  Gehororgan  der  Wirbeltiere,  Stockholm. 

ScHONEMANN,  A.  1904.  Die  Topographic  des  menschlichen  Gehoror- 
ganes,  Wiesbaden. 

Shambaugh,  G.  E.  1907.  A  Restudy  of  the  Minute  Anatomy  of 
Structures  in  the  Cochlea  with  Conclusions  Bearing  on  the  Solution  of  the 
Problem  of  Tone  Perception,  Am.  Jour.  Anat.,  vol.  vii. 


THE    AUDITORY    APPARATUS  227 

Shambaugh,  G.  E.  1908.  Tho  Memlnana  Tectoria  and  the  Theory 
of  Tone  Perception,  Arch.  Otology,  vol.  x.xxvii. 

— .  1910.  Das  Verhiiltnis  zwischen  der  Membrana  Tectoria  und  dem 
Cortischen  Organ,  Zeits.  f.  Ohrenheilk.,  Bd.  62. 

— .  1912.  Ueber  den  Bau  und  die  Funktion  der  Crista  AmpuUaris, 
Ibid.,  Bd.  (35. 

Streeter,  G.  L.  1907.  On  the  Development  of  the  Membranous 
Labyrinth  and  the  Acoustic  and  Facial  Nerves  in  the  Human  Embryo, 
Amer.  Jour.  Anat.,  vol.  vi. 

Van  der  Stricht,  O.  1918.  The  Genesis  and  Structure  of  the  Mem- 
brana Tectoria  and  the  Crista  Spiralis  of  the  Cochlea,  Carnegie  Inst,  of 
Washington,  Contr.  to  Embryology,  No.  21,  pp.  ,57-86. 

Watson,  J.  B.  1914.  Behavior,  An  Introduction  to  Comparative 
Psychology,  New  York,  Chapter  XII. 


CHAPTER  XIV 


THE  VISUAL  APPARATUS 


The  eye  is  the  most  highly  specialized  sense  organ  in  the 
human  body,  and  in  other  respects  it  occupies  a  very  unique 
position.  The  essential  receptive  part  of  the  eye  is  in  the  ret- 
ina. But  the  retina  is  much  more  than  this;  it  is  really  a  part 
of  the  brain,  and  the  so-called  optic  nerve  is  a  true  cerebral 
tract.  This  is  evident  from  a  consideration  of  the  embryo- 
logic  development  of  the  retina. 

In  the  early  embryonic  stages  the  neural  tube  expands  laterally  in  the 
position  of  the  future  thalamus,  and  from  the  upper  part  of  this  region  a 
"primary  optic  vesicle"  is  evaginated  from  the  lateral  wall  on  each  side 

Optic  cup 
Optic  stalk   I  Lens  rudiment 


Cavity  of  forebrain 


Ectoderm  forming  lens 
rudiment 


Optic  vesicle  becoming 
cupped 

Fig.  97. — Diagraniiuatic  section  through  the  head  of  a  fetal  rabbit  to 
illustrate  the  mode  of  formation  of  the  primary  and  secondary  optic  vesicles 
and  of  the  lens  of  the  eye.  The  right  side  of  the  figure  is  drawn  from  a  more 
advanced  stage  than  the  left  side.      (From  Cunningham's  Anatomy.) 

.(Figs.  46,  47,  49,  97).  The  optic  vesicle  grows  outward  toward  the  skin 
and  assumes  the  form  of  a  hollow  sphere,  whose  cavity  remains  in  com- 
munication with  that  of  the  third  ventricle  by  a  hollow  stalk  (Fig.  97). 
While  the  formation  of  the  primary  optic  vesicle  is  in  progress  the  over- 
lying ectoderm  (outer  skin)  is  thickened  and  finally  invaginated  to  form 
the  lens  of  the  eye,  the  optic  vesicle  collapses  so  that  its  cavity  is  oblitei'- 
ated  by  the  apposition  of  its  lateral  and  medial  walls,  and  a  secondary 
cavity  (the  secondary  optic  vesicle  or  optic  cup)  is  formed  whose  walls  are 
two-layered,  being  composed  of  both  the  original  lateral  and  medial  parts 

228 


THE    VISUAL    APPARATUS  229 

of  the  priinais'  optic  vesicle  (Fig.  97,  uii  the  right  side).  Thi.s  .secondary 
cavitj-  contains  the  vitreous  humor  in  the  adult  eye;  the  layer  of  the  sci"- 
ondary  optic  vesicle  which  borders  the  vitreous  humor  forms  the  retina; 
the  outer  layer  of  the  vesicle  forms  the  pigment  layer  of  the  retina;  and 
the  stalk  forms  the  optic  nerve  by  the  ingrowth  of  fibers  throughout  its 
length  from  the  retina  and  brain  (Fig.  100). 

The  retina,  then,  is  as  tiiily  a  part  of  the  brain  as  is  the 
cerebral  hemisphere  and  its  structure  is,  in  general,  similar 
to  that  of  other  parts  of  the  brain.  There  are  supportino; 
cells,  the  fibers  of  ]\Iuller  (Fig.  98,  M),  and  neuroglia  elements 
(Fig.  98,  d.s.  and  s.s.),  and  bang  among  these  are  the  neurons. 
The  latter  can  be  classified  in  general  in  four  groups:  (1) 
the  rods  and  cones  (Fig.  98,  .4);  (2)  the  bipolar  cells  (Fig.  98. 
D);  (3)  the  so-called  ganglion  cells  which  give  rise  to  fibei-s 
of  the  optic  nerve  (Fig.  98,  F);  (4)  horizontal^  disposed  cor- 
relation neurons  (Fig.  98,  h).  All  of  these  tA'pes  except  the 
third  are  intrinsic  to  the  retina,  i.  e.,  they  send  none  of  their 
fibrous  processes  beyond  the  limits  of  the  retina  itself.  The 
axons  of  the  neurons  of  the  third  type  pass  out  of  the  retina 
and  form  the  so-called  optic  nerve,  terminating  in  the  thalamus 
or  midbrain. 

Immediatel}''  external  to  the  nervous  la3'er  of  the  retina  is  the 
pigment  layer  (Figs.  99.  100),  which  is  formed  from  the  outer 
epithelial  layer  of  the  secondar}-  optic  vesicle  (Fig.  97). 
Figure  99  illustrates  the  ten  layers  of  the  retina  as  figured 
by  the  older  histologists,  and  Fig.  98  illustrates  the  relations 
of  some  of  the  nervous  elements  as  revealed  by  the  Golgi 
method.  It  is  evident  that  the  '^nuclear"  or  "granular" 
layers  are  characterized  chiefly  by  the  presence  of  the  cell 
bodies  of  the  neurons  and  their  nuclei,  while  the  "molecular" 
layers  are  composed  chiefly  of  the  fibrillar  nerve-endings 
which  form  the  synapses  between  the  various  groups  of 
neurons. 

The  rods  and  cones  of  the  retina  are  the  receptors  and  also 
the  neurons  of  the  first  order  in  the  optic  path.  Their  free  ends 
project  through  the  external  limiting  membrane  into  the 
pigment  layer.  Rays  of  light  which  pass  through  the  dioptric 
apparatus  (lens,  humors,  etc.)  of  the  eyeball  must  penetrate 
also  the  entire  thickness  of  the  retina  (which  is  very  trans- 
parent) before  they  reach  these  receptors  (Fig.  100). 


230 


INTRODUCTION    TO    NEUROLOGY 


Fig.  98. — Two  transverse  sections  through  the  mammalian  retina:  A, 
Layer  of  rods  and  cones;  ar,  internal  arlaorizations  of  bipolar  neurons  related 
to  the  cones;  ar',  internal  arborizations  of  bipolar  neurons  related  to  the 
rods;  B,  outer  nuclear  layer;  C,  outer  molecular  layer;  c,  cones;  c.c,  contact 
of  bipolar  neurons  with  branches  of  the  cone  fibers;  c.b.,  bipolar  neurons 
related  to  cones;  eg-,  cone  granules  or  nuclei  of  cones;  c.n.,  centrifugal  nerve- 
fiber;  c.r.,  contact  of  bipolar  neurons  with  ends  of  rod  fibers;  D,  inner  nuclear 
layer;  d.s.,  diffuse  neuroglia  elements;  E,  inner  molecular  layer;  F,  ganglionic 
layer;  G,  layer  of  nerve-fibers;  g,  neurons  of  the  ganglionic  layer;  h,  horizontal 
cells;  M,  supporting  fiber  of  Miiller;  r,  rods;  r.b.,  bipolar  neurons  related  to 
rods;  r.g.,  rod  granules  or  nuclei  of  rods;  s.g.i  stratified  ganglion  cells;  s.s., 
stratified  neuroglia  elements.     (After  Ramon  y  Cajal.) 


THE   VISUAL    APPARATUS 


231 


The  peripheral  ends  of  the  rods  contain  a  pigment,  the 
visual  purple  or  rhodopsin,  which  is  chemically  changed  by 
light  ra3^s  and  has  been  supposed  to  function  as  the  exciting 
agent  for  nervous  impulses  of  sensibility  to  light  in  the  rod 
cells.  But  recent  experiments  go  to  show  that  the  visual 
purple  is  concerned  with  the  adaptation  of  the  eye  to  different 

Istratum 
f  pigmenti 


Gangli- 
onic 
I  layer 

Istratum 
[opticura 

Membrana  liniitans  interna 
Fig.  99. — Ditigranuiiiitic   section   through   the   human  retina    to  illustrate 
the  ten  hiyers  as  commonly  enumerated.      (After  Schultze,   from  Cunning- 
ham's Anatomy.) 

intensities  of  light  rather  than  with  the  specific  receptor  func- 
tion itself.  The  brown  pigment  of  the  pigment  layer  is 
probably  also  concerned  with  light  adaptation. 

The  exact  mechanism  through  the  agency  of  which  the  rods 
and  cones  are  excited  to  nervous  activity  by  light  is  still 
obscure;  but  when  the  rods  and  cones  are  once  actuated,  they 


232 


INTRODUCTION    TO    NEUROLOGY 


may  transmit  their  nervous  impulses  across  synapses  in  the 
external  molecular  layer  to  neurons  of  the  second  order  whose 
cell  bodies  lie  in  the  internal  granular  layer.  The  neurons 
of  the  internal  granular  layer  are  of  diverse  sorts,  some  of 
them  spreading  the  nervous  impulse  laterally  (probably  for 
summation  effects  in  weak  illumination),  but  most  of  them 
conducting  radially  and  effecting  synaptic  connection  with 
the  dendrites  of  the  ''ganglion  cells  of  the  retina."  The  latter 
are  neurons  of  the  third  order  whose  axons  form  the  larger 


Fig.  100. — Diagram  of  the  relations  of  the  retina  and  the  so-called 
optic  nerve  to  the  other  parts  of  the  brain. 


part  of  the  fibers  of  the  so-called  optic  nerve,  which  is  really 
not  a  peripheral  nerve  at  all,  but  a  true  cerebral  tract. 

The  fibers  of  the  ''optic  nerve,"  having  reached  the  ventral 
surface  of  the  brain,  enter  the  optic  chiasma,  where  part  of 
them  cross  to  the  opposite  side  of  the  brain,  while  others  enter 
the  "optic  tract"  of  the  same  side.  From  the  chiasma  a  big 
tract  of  crossed  and  uncrossed  optic  fibers  passes  upward  and 
backward  across  the  surface  of  the  thalamus,  where  they 
divide  into  two  groups.  Some  terminate  in  the  pulvinar 
and  lateral  geniculate  body  which  form  the  postero-dorsal 
part  of  the  thalamus  (Figs.  45,  76,  77) ;  others  pass  these 
structures  to  end  in  the  roof  of  the  superior  colliculus  of  the 
midbrain,  i.  e.,  in  the  optic  tectum.     The  latter  connection 


THE   VISUAL    APPARATUS  23^^ 

is  for  responses  of  purely  reflex  type,  chiefly  those  concerned 
with  the  movements  of  the  eyeballs  and  accommodation  of 
the  eyes;  the  thalamic  connection  is  a  station  in  the  cortical 
visual  path. 

From  these  relations  it  follows  that  there  is  nothing  in  the 
visual  organs  which  corresponds  to  a  peripheral  nerve.  The 
retina  as  a  part  of  the  brain  is  directly  excited  by  the  light 
waves  which  penetrate  its  substance.  The  so-called  optic 
nerve  is  a  tract  within  the  brain,  whose  fibers  for  the  most 
part  come  from  visual  neurons  of  the  third  order  in  the  retina, 
though  there  are  others  also  which  come  from  the  brain  and 
pass  outward  to  end  by  free  arborizations  within  the  retina 
(Fig.  98,  c.n.).  The  function  of  these  centrifugal  fibers  to 
the  retina  is  unknown.  Identically  the  same  nerve-fibers 
which  make  up  the  so-called  optic  nerves  peripherally  of  the 
optic  chiasma  are  called  the  optic  tracts  centrally  of  that  point. 
It  would  be  more  logical  to  name  these  fibers  optic  tracts 
for  their  entire  length,  these  tracts  being  very  similar  to  those 
of  the  lemniscus  systems.  Like  the  lemniscus  fibers,  they 
decussate  completely  in  the  optic  chiasma  in  lower  verte- 
brates before  terminating  in  the  thalamus  and  midbrain. 
It  is  only  in  animals  with  an  overlapping  of  the  fields  of  vis- 
ion of  the  two  eyes  and  stereoscopic  vision  that  the  decussa- 
tion of  the  optic  tracts  in  the  chiasma  is  incomplete. 

The  significance  of  the  crossed  and  uncrossed  fibers  of  the 
optic  tracts  is  seen  in  Fig.  101.  .  In  this  diagram  the  shaded 
portions  of  the  retinae  receive  their  light  from  the  left  side  of 
the  median  plane  of  the  body;  the  unshaded  portions,  from 
the  right  side.  The  nasal  part  of  each  retina  receives  visual 
images,  from  objects  lying  in  the  same  side  of  the  body  exclu- 
sively, i.  e.,  from  the  temporal  portion  of  the  visual  field, 
while  the  temporal  part  of  the  retina  maj^  receive  images  from 
objects  on  the  opposite  side  of  the  body.  Accordingly,  in 
order  that  the  visual  images  derived  from  all  objects  lying 
on  one  side  of  the  body  may  be  represented  by  nervous 
excitations  within  the  opposite  half  of  the  brain,  it  is  necessary 
that  the  nerve-fibers  from  the  nasal  part  of  each  retina  cross 
in  the  chiasma,  while  those  from  the  temporal  part  pass 
through  the  chiasma  without  decussation. 


234 


INTRODUCTION    TO    NEUROLOGY 


tiiS^H! 


V^^Fieiafj. 


""'i^lLo^e 


Fig.  101.  • 


THE   VISUAL    APPARATUS  235 

The  reflex  optic  centers  in  the  roof  of  I  ho  midbrain  occupy 
most  of  the  colliculiis  superior,  which  corresponds  to  the  optic- 
lobe  of  the  fisli  brain  (Figs.  43,  44).  Here  visual  impressions 
are  brought  into  physiological  relations  with  those  of  the 
tactual  and  auditory  systems  received  by  the  lemnisci.  The 
chief  efferent  pathwaj'  from  this  center  is  by  way  of  the  under- 
lying cerebral  peduncle  (Fig.  75).  Here  reflex  connections 
are  effected  directly  with  the  nuclei  of  the  III  and  IV  cranial 
nerves  for  the  eye  muscles,  and  through  the  fasciculus  longi- 
tudinalis  medialis  with  the  centers  for  all  other  cranial  and 
spinal  muscles.  This  fasciculus  is  a  strong  bundle  composed  of 
both  descending  and  ascending  fibers  whose  function  is  the 
general  coordination  of  reflex  motor  responses,  and  in  par- 
ticular those  of  the  conjugate  movements  of  the  two  eyes 
(see  p.  203).  Reflex  movements  of  the  muscles  of  the  trunk 
and  limbs  in  response  to  visual  stimuli  are  effected  chiefly 
through  the  tecto-spinal  tract,  this  tract  conveying  fibers 
also  for  auditory  reflexes  from  the  inferior  colliculus  (p.  225). 

The  accommodation  of  the  eye  for  distance  is  effected  by 
changes  in  the  curvature  of  the  lens,  and  the  adaptation  for 
differences  in  illumination  is  effected  in  part  by  changes  in  the 
diameter  of  the  pupil  (this  is  in  addition  to  the  changes  in  the 
retinal  pigment  referred  to  on  p.  231  and  to  changes  in  the  rods 
and  cones  and  other  neurons  of  the  retina  which  may  be  excited 
by  the  centrifugal  fibers  from  the  brain  to  the  retina  referred  to 
on  p.  233).  The  nerves  controlling  the  movements  of  the  lens 
and  the  pupillary  reactions  belong  to  the  visceral  motor  sj^s- 
tem.  They  leave  the  central  nervous  system  in  part  through 
the  oculomotor  nerve  and  in  part  (for  dilation  of  the  pupil) 
from  the  lower  cervical  region  of  the  spinal  cord.  The  latter 
fibers  pass  by  way  of  roots  of  spinal  nerves  into  the  superior 
cervical  sympathetic  ganglion  (p.  261  and  Fig.  41,  p.  115) 
and  then  forward  to  the  eyeball.     We  cannot  here  enter  into 

Fig.  101. — A  diagram  of  the  -sdsual  tract,  illustrating  the  significance  of 
the  partial  decussation  of  nerve-fibers  in  the  optic  chiasma  so  as  to  ensure 
the  representation  in  the  cerebral  cortex  of  nervous  impulses  excited  by  ob- 
jects on  the  opposite  half  of  the  body  onlj-.  Ill,  Oculomotor  nerve;  L, 
medial  lemniscus;  M,  mammillary  bodies;  RN,  red  nucleus  (nucleus  ruber); 
.S.V,  black  substance  (substantia  nigra);  TG,  optic  tract  to  corpora  quadri- 
gemina  (cf.  Fig.  75).      (From  Starr's  Nervous  Diseases.) 


236  INTRODUCTION  TO  NEUROLOGY 

further  details  of  the  mechanism  of  accommodation  or  of  the 
dioptric  apparatus  and  the  accessory  parts  of  the  eye;  see 
the  larger  text-books  of  anatomy  and  physiology. 

The  thalamic  connections  of  the  optic  tracts  in  the  lowest 
vertebrates  are  very  insignificant,  collaterals  of  these  fibers 
being  given  off  to  terminate  in  the  unspecialized  correlation 
centers  of  the  dorsal  part  of  the  thalamus.  But  in  all  forms 
with  a  differentiated  cerebral  cortex  these  thalamic  optic  con- 
nections assume  greater  importance,  a  special  region  in  the  dor- 
sal part  of  the  thalamus  being  set  apart  for  their  use.  Thus 
arose  the  lateral  geniculate  body,  and  in  higher  mammals  this 


Fig.  102. — Section  through  the  parietal  eye  of  a  lizard  (Anguis  fragilis) : 
ct,  connective-tissue  cells  around  nerve;  gc,  ganglion  cells;  Z,  lens;  n,  nerve- 
fibers;  PC  pigment  cells;  pn,  parietal  nerve  from  the  parietal  eye  to  the  brain; 
r,  retinal  cells;  vb,  vitreous  body.     (After  Nowikoff.) 

is  supplemented  by  the  pulvinar.  These  centers  are,  in  the 
strict  sense  of  the  word,  cortical  dependencies,  for  they  attain 
to  only  very  insignificant  proportions  in  forms  with  rudimen- 
tary cerebral  cortex,  but  increase  in  proportion  to  the  elabora- 
ting of  the  visual  cortex  (see  p.  122). 

The  early  steps  in  the  evolution  of  the  eyes  of  vertebrates  are  imper- 
fectly understood.  In  structure  and  mode  of  function  the  vertebrate 
eyes  are  unhke  those  of  any  of  the  invertebrate  animals.  The  experi- 
ments of  Parker  and  others  have  shown  that  the  skin  of  many  aquatic  ver- 
tebrates among  the  fishes  and  amphibians  is  sensitive  to  light,  and  it  has 
been  supposed  that  the  vertebrate  retina  was  differentiated  from  such 


THE   VISUAL    APPARATUS  237 

cutaneous  photoreceptors.  But  it  seems  more  probable  (Parker,  1908) 
that  the  vertebrate  organs  of  vision  were  developed  from  the  first  within 
the  central  nervous  system. 

Some  of  the  fishes  and  reptiles  possess,  in  addition  to  lateral  eyes  of 
typical  form,  a  jnedian  eye,  the  parietal  or  pineal  eye  (Fig.  102),  which  is 
developed  from  a  tubular  outgrowth  from  the  roof  of  the  diencephalon  (the 
pineal  organ  or  epiphysis,  p.  177);  this  extends  dorsalward  from  the  brain 
through  a  special  foramen  in  the  skull  to  reach  the  skin  in  the  center  of 
the  top  of  the  head.  The  functions  and  evolutionary  significance  of  this 
eye  are  shrouded  in  mystery. 

Summary. — The  retina  is  developed  as  a  lateral  outgrowth 
from  the  early  neural  tube  and  throughout  life  retains  its  char- 
acter as  a  part  of  the  brain,  the  "optic  nerve"  being  really  a 
correlation  tract  comparable  with  the  lemniscus  systems.  The 
rods  and  cones  of  the  retina  are  the  photoreceptors  and  also  the 
neurons  of  the  first  order  in  the  optic  path.  The ''  optic  nerve" 
contains  neurons  of  the  third  order  from  the  retina  to  the  thala- 
mus and  midbrain,  and  also  centrifugal  fibers  from  the  mid- 
brain to  the  retina.  In  lower  vertebrates  the  fibers  of  the  optic 
path  decussate  completely  in  the  optic  chiasma,  but  in  those 
mammals  whose  fields  of  vision  overlap  there  is  an  incomplete 
decussation  so  as  to  ensure  the  representation  of  the  field  of 
vision  of  one  side  completely  in  the  opposite  cerebral  hemi- 
sphere. Those  fibers  of  the  optic  tract  which  terminate  in  the 
midbrain  effect  various  kinds  of  reflex  connections,  while  those 
which  terminate  in  the  thalamus  effect  cortical  connections. 
The  parietal  or  pineal  eye  of  some  fishes  and  reptiles  is  appai- 
ently  functional  as  an  organ  of  vision  which  was  developed 
quite  independently  of  the  lateral  eyes. 

Literature 

In  this  chapter  we  have  not  attempted  to  present  a  systematic  descrip- 
tion of  the  structure  of  the  eye  or  of  the  functions  of  the  retina  and 
theories  of  vision.  For  the  details  of  these  questions  reference  must  be 
niade  to  the  larger  text-books  of  anatomy,  physiologj^,  and  physiological 
psychology.  A  few  general  works  aie  cited  below,  together  with  some 
special  reseai'ches  to  which  reference  has  been  made  in  the  preceding  text : 

VON  Bechterew,  W.  1909.  Die  Funktionen  der  Nervencentra,  Jena, 
Bd.  2,  pp.  996-1103.     Idem,  1911,  Bd.  3,  pp.  1554-1583,  1883-1964. 

Cole,  L.  J.  1907.  An  Experimental  Study  of  the  Imnge-forming 
Powers  of  Various  Types  of  Eyes,  Proc.  Amer.  Acad.  Arts  and  Sciences, 
vol.  xlii.  No.  16. 

Harris,  W.  1904.  Binocular  and  Stercosc-opic  ^  ision  in  Alan  an<l 
Other  Vertebrates,  with  Its  Relation  to  tlie.  Decussation  of  tlio  Optic 


238  INTRODUCTION   TO    NEUROLOGY 

Nerves,  the  Ocular  Movements,  and  the  Pupil  Light  Reflex,  Brain,  vol. 
xxvii,  pp.  106-147. 

Ladd,  G.  T.,  and  Woodworth,  R.  S.     1911.     Elementsof  Physiological 
Psychology,  New  York. 

Mast,  S.  O.     1911.     Light  and  the  Behavior  of  Organisms,  New  York. 

NuEL,  J.  P.     1904.     La  Vision,  Bibliotheque  Internationale  de  Psy- 
chologie  Experimental  Normal  et  Pathologique,  Paris. 

Pakker,  G.  H.     1908.     The  Origin  of  the  Lateral  Eyes  of  Vertebrates, 
Amer.  Nat.,  vol.  xlii,  pp.  601-609. 

— .  1909.  The  Integumentary  Nerves  of  Fishes  as  Photoreceptors  and 
Their  Significance  for  the  Origin  of  the  Vertebrate  Eyes,  Amer.  Jour,  of 
Physiol.,  vol.  xxv,  pp.  77-80. 

Ramon  y  Cajal,  S.     1894.     Die  Retina  der  Wirbeltiere,  Wiesbaden. 

ScHAFER,  E.  A.     Text-book  of  Physiology,  vol.  ii,  pp.  752-761,  1026- 
1148. 

Vincent,  S.  B.     1912.     The  Mammalian  Eye,  Jour.  Animal  Behavior, 
vol.  ii,  pp.  249-255. 

Watson,  J.  B.     1914.     Behavior,  an  Introduction  to  Comparative  Psy- 
chology, New  York,  Chapter  XL 


CHAPTER  XV 
THE  OLFACTORY  APPARATUS 

The  olfactory  ptiit  of  the  brain  as  a  whole  is  sometimes  called 
the  rhinencephalon.  In  fishes  (p.  118  and  Figs.  43,  44)  almost 
the  whole  of  the  cerebral  hemisphere  is  devoted  to  this  func- 
tion, and  as  we  pass  up  the  scale  of  animal  life  more  and  more 
non-olfactory  centers  are  added  to  the  hemisphere  in  the  corpus 
striatum  and  cerebral  cortex,  until  in  man  the  non-olfactorj^ 
part  of  the  hefnisphere  overshadows  the  rhinencephalon.  The 
complex  form  of  the  human  cerebral  hemisphere  cannot  be 
adequately  understood  apart  from  a  knowledge  of  this  evolu- 
tionary history,  which  has  been  studied  with  great  care  by 
comparative  neurologists.  The  metamorphosis  of  the  verte- 
brate cerebral  hemisphere  from  a  simple  olfactory  reflex 
apparatus  in  the  lower  fishes  to  the  great  organ  of  the  higher 
mental  processes  upon  which  all  human  culture  depends  is  a 
very  dramatic  history,  into  which,  unfortunately,  we  cannot 
here  enter. 

Smell  is  evidently  the  dominant  sense  in  manj^  of  the  lower 
vertebrates.  That  this  is  the  case  in  the  dogfish  is  shown  by 
the  enormous  development  of  the  olfactory  centers  of  the  brain, 
to  which  reference  has  just  been  made.  And  in  most  of  the 
laboratory  mammals,  such  as  the  rat  and  the  dog,  the  sense 
of  smell  still  plays  a  very  much  more  important  part  in  the 
behavior  complex  than  in  man  and  other  primates,  whose 
olfactory  organs  are  in  a  reduced  condition. 

The  nervus  terminalis  is  a  slender  ganglionated  nerve  found  associated 
with  the  olfactory  nerve  in  most  classes  of  vertebrates  from  fishes  to  man. 
Its  fi]:)ers,  which  are  unmyelinated,  reach  the  mucous  membrane  of  the 
nose,  thougli  the  precise  method  of  their  ending  is  unknown.  They  pass 
inward  in  company  with  those  of  the  olfactory  nerve  as  far  as  the  olfac- 
tory bulb.  Here  they  separate  from  the  olfactory-  fillers  and  enter  the 
cerebral  hemisphere  between  the  attachment  of  the  olfactory  bulb  and  the 
lamina  terminalis  (Fig.  43,  p.  119).  Within  the  brain  they  have  been 
followed  backward  in  Amphibia  through  the  entire  length  of  the  olfactory 

2.39 


240 


INTRODUCTION    TO    NEUROLOGY 


area  and  hypothalamus,  but  their  cerebral  connections  have  never  been 
accurately  determined.  The  function  of  this  nerve  is  likewise  whoUj- 
unknown. 

In  man  the  terminal  nerve  is  widely  distributed  to  the  olfactory  mu- 
cous membrane  of  the  nose  by  numerous  slender  filaments  which  anasto- 
mose freely  with  each  other  and  are  distinct  from  those  of  the  olfac- 
tory nerve  with  which  they  are  mingled.  Numerous  ganglion  cells  are 
scattered  among  them,  especially  in  a  more  densely  aggregated  ganglion 
terminale  near  the  olfactory  bulb.  There  are  approximately  1500  of 
these  cells  on  each  side  of  the  body.  Having  entered  the  cranial  cavitj', 
the  nervus  terminalis  passes  by  the  olfactory  bulb  and  extends  farther 
backward,  usually  in  several  very  slender  strands  embedded  in  the  pia 
mater  over  the  gyrus  rectus,  to  enter  the  brain  substance  at  or  near  the 
anterior  liorder  of  the  medial  olfactory  stria  (see  Fig.  105).  For  more 
complete  descriptions  see  the  works  of  Brookover,  Johnston,  McCotter, 
and  Huber  and  Guild  cited  at  the  end  of  this  chapter. 

In  the  nose  of  most  vertebrates  there  is  a  special  region  containing  a 
portion  of  the  olfactory  sensory  epithelium  known  as  the  vomeronasal 
organ,  or  organ  of  Jacobson.  This  receives  a  special  slip  of  the  olfactory 
nerve,  the  vomeronasal  nerve,  and  in  some  animals  a  special  accessory 
olfactory  bulb  is  developed  in  the  brain  to  receive  this  nerve  (seethe 
papers  by  McCotter).  This  apparatus  is  well  developed  in  the  frog  and 
from  the  accessory  olfactory  bulb  a  special  olfactory  tract  is  directed  into 
the  nucleus  amj^gdalse  in  the  corpus  striatum  complex. 

The  olfactory  cerebral  centers  fall  into  two  groups:  (1)  the 
reflex  centers  of  the  brain  stem  and  (2)  the  olfactory  cerebral 
cortex.  The  arrangements  of  the  olfactory  reflex  centers  and 
their  connecting  tracts  are  essentially  similar  in  plan  in  all  ver- 
tebrate brains  (except  in  some  aquatic  mammals,  like  the  dol- 
phin, which  lack  olfactory  organs  altogether).  The  olfactory 
cerebral  cortex,  on  the  other  hand,  is  very  diversely  developed 
in  different  groups  of  vertebrates.  There  is  no  true  cerebral 
cortex  in  fishes;  in  amphibians  (particularly  in  the  frog)  the 
olfactory  cerebral  cortex  begins  to  emerge  from  the  general 
olfactory  reflex  centers;  in  reptiles  there  is  a  well-formed 'olfac- 
tory cortex  of  simple  histologic  pattern  and  the  beginnings  of 
the  non-olfactory  cortex;  in  birds  the  olfactory  apparatus  is 
reduced  and  the  non-olfactory  cortex  is  somewhat  more 
extensive  than  in  reptiles;  in  mammals  both  the  olfactory 
cerebral  cortex  and  the  non-olfactory  cortex  attain  their 
maximum  dimensions,  the  former  in  the  lowest  members  of 
this  group  a,nd  the  latter  in  the  highest. 

The  cerebral  cortex  as  a  whole  is  sometimes  called  the 
pallium.  That  portion  of  the  pallium  which  is  related  with  the 
olfactory  apparatus  was  dijfferentiated  earlier  in  vertebrate  evo- 


THE  OLFACTORY  APPARATUS 


241 


liition  than  the  non-olfactory  pallium  and  has,  therefore,  been 
called  the  archijjallmm.  The  non-olfactory  cerebral  cortex  is 
termed  the  neo'pallium  (or  somatic  pallium,  for  it  receives  the 
somatic  projection  fibers).  The  archipallium,  as  already  indi- 
cated, attains  its  maximum  development  in  the  lowest  mam- 
mals, particularly  the  marsupials,  like  the  kangaroo  and  opos- 
sum, consisting  of  the  hippocampus  and  hippocampal  gyrus 
(gyrus  hippocampi,  or  pyriform  lobe).  The  neopallium  at- 
tains its  maximum  size  in  the  human  brain,  and  the  indications 
are  that  in  civilized  races  it  is  now  in  process  of  furthei-  differ- 


Fig.  103. — Dissection  of  the  right  olfactory  bulb  and  nerve  on  the  lateral 
wall  of  the  nasal  cavity.  (From  Wood's  Reference  Handbook  of  the  Medical 
Sciences.) 

entiation.  In  the  human  brain  practically  all  parts  of  the 
exposed  cerebral  cortex  are  neopallium,  the  archipallium  being 
of  relatively  small  size  and  mostly  concealed  by  a  process  of 
infolding  along  the  posterior  margin  of  the  neopallium. 

In  the  human  body  the  specific  olfactory  receptors  (see  p.  97) 
are  limited  to  a  small  area  of  the  mucous  lining  in  the  upper 
part  of  the  nasal  cavity  on  both  its  lateral  (Fig.  103)  and  its 
medial  walls.  The  cell  bodies  of  the  olfactory  neurons  of  the 
first  order  lie  in  this  mucous  membrane  (Figs.  36  and  104). 
The  axons  of  these  neurons  form  the  fibers  of  the  olfactory 
nerve,  which  are  unmyelinated;  they  pierce  the  ethmoid  bone 
16 


242 


INTRODUCTION   TO    NEUROLOGY 


in  numerous  small  fascicles  (fila  olfactoria)  and  terminate  by 
free  arborizations  in  the  primary  olfactory  center  within  the 
olfactory  bulb  (Figs.  53,  78,  103,  104).  Several  olfactory 
nerve-fibers  terminate  together  in  a  dense  entanglement  of 
fibers  termed  a  glomerulus,  which  also  receives  one  or  more 
dendrites  from  the  olfactory  neurons  of  the  second  order,  or 
mitral  cells.  The  glomerulus,  therefore^  contains  the  first 
synapse  in  the  olfactory  pathway.  The  axons  of  the  mitral 
cells  form  the  olfactory  tract  and  discharge  into  the  olfactory 
area,  or  secondary  olfactory  nucleus,  at  the  base  of  the  ol- 
factory bulb.  These  axons  give  off  collateral  branches  which 
discharge  among  very  small  neurons  of  the  olfactory  bulb, 


Olfactory  tract 


Glomerulas 
Olfactory  nerve 
Ethmoid  bone 
Olfactory  epithelium 

Fig.   104. — Diagram  of  the  connections  of  the  olfactory  bulb. 

the  granule  cells,  whose  chief  processes  are  directed  peripheral- 
ward,  to  end  among  dendrites  of  the  mitral  cells. 

Attention  has  already  been  called  (pp.  80  and  97)  to  the  fact 
that,  though  smell  and  taste  are  both  chemically  excited  senses, 
the  olfactory  organs  can  be  excited  by  much  more  dilute  solu- 
tions of  the  stimulating  substances  than  can  the  gustatory  or- 
gans. The  lowering  of  the  threshold  for  olfactory  stimuli  has 
been  effected  by  several  means,  among  which  we  may  mention 
the  following:  Whereas  in  the  taste-buds  there  is  a  synapse 
between  the  specific  receptor  cells  and  the  peripheral  nerve- 
fiber  (Fig.  35,  p.  96),  there  is  no  such  synapse  in  the  olfactory 
organ,  the  peripheral  receptor  cell  giving  rise  directly  to  the 
olfactory  nerve-fiber   (Fig.   104).    In  the  second    place,  the 


THE  OLFACTORY  APPARATUS 


243 


peripheral  gustatory  nerve-fiber  discharges  centrally  into 
several  neurons  of  the  primary  gustatory  center  in  the  medulla 
oblongata;  but  many  peripheral  olfactory  fibers  enter  a  single 
glomerulus,  where  they  are  engaged  by  dendrites  from  only 
one  or  two  mitral  cells,  thus  providing  for  the  summation  of 
stimuli  in  each  mitral  cell.  Again,  the  collateral  discharge 
from  the  olfactory  tract  into  the  granule  cells  (which  are  very 
numerous)  carries  the  discharge  from  the  mitral  cells  back 
again  into  these  cells  and  thus  reinforces  their  discharge  (see 
pp.  107,  214).    By  these  and  other  devices  exceedingly  feeble 


Olfactory  bulb 


Lateral  olfactory  gyrus 
(stria) 

Posterior  parolfactory, 
sulcus 

Uncus  (hippocampal. 
gyrus) 


Medial  olfactory  gyrus  (stria) 
Olfactory  tract 

Limen  insulae 

Anterior  perforated 
substance 

Hippocampal  gyrus 


Fig.  105. — Brain  of  a  human  fetus  at  the  beginning  of  the  fifth  month 
(22.5  cm.  long),  illustrating  the  olfactory  centers  visible  on  the  ventral 
surface.      (After  Retzius,  from  Morris'  Anatomy.) 


peripheral  stimuli  ma}^  give  rise  to  very  strong  excitations 
in  the  olfactory  centers. 

The  fibers  of  the  olfactory  tract  reach  the  olfactory  area,  or 
secondary  center,  by  three  paths  which  spread  out  from  the 
base  of  the  olfactory  bulb  and  are  known  as  the  medial,  inter- 
mediate, and  lateral  olfactory  striae  (these  are  shown  but  not 
named  on  Fig.  53,  p.  129).  The  olfactory  area  has  various 
subdivisions  (Fig.  105),  the  most  important  of  which  are:  (1) 
the  lateral  olfactory  nucleus  (or  gja-us)  which  receives  the 
lateral  olfactory  stria  and  extends  backward  directly  into  the 


244 


INTRODUCTION   TO    NEUKOLOGY 


tip  of  the  temporal  lobe  of  the  cerebral  cortex  (uncus),  where 
the  ventro-lateral  ends  of  the  hippocampus  and  the  hippo- 
campal  gyrus  come  together ;  (2)  the  medial  olfactory  nucleus, 
including  the  subcallosal  gyrus  (Fig.  52,  p.  128)  and  septum, 
which  receive  the  medial  olfactory  stria;  (3)  the  intermediate 
olfactory  nucleus,  which  occupies  the  anterior  perforated 
substance   (Figs.  53,   105)  and  receives  the  intermediate  ol- 


form.  bi 


Troll.  hypthN       \n.pop. 


Fig.  106. — Diagram  of  some  of  the  olfactory  tracts  in  the  brain  of  the 
rat.  The  chief  connections  of  the  medial  and  intermediate  olfactory  tracts 
are  indicated;  those  of  the  lateral  olfactory  tract  are  omitted:  c.mam.,  corpus 
mamillare;  col.  forn.,  columna  fornicis;  com.  ant.,  commissura  anterior;  com. 
hip.,  commissura  hippocampi;  com.  post.,  commissura  posterior;  form,  bidh., 
formatio  bulbaris;  /.  rdr.,  fasciculus  retroflexus  of  Meynert;  hab.,  habenula, 
h.pc,  hippocampus  precommissuralis;  h.sc,  hippocampus  supracommis- 
suralis;  n.  ant.,  nucleus  anterior  thalami;  n.  olf.  ant.,  nucleus  olfactorius 
anterior;  n.  pop.,  nucleus  preopticus  (ganglion  opticum  basale) ;  S,  septum; 
str.  med.,  stria  meduUaris  thalami;  fr.  mam.  th.,  tractus  mamillo-thalamicus 
(Vicq  d'Azyri) ;  tr.  olf.  hypth.,  tractus  olfacto-hypothalamicus,  or  basal  ol- 
factory tract;  tr.  olf.  tegm.,  tractus  olfacto-tegmentalis;  tub.  f.  dent.,  tuberculum 
fasciae  dentatse  (hippocampus  postcommissuralis) ;  tub.  olf.,  tuberculum 
olfactorium. 

factory  stria.  These  nuclei  are  all  important  rejflex  centers, 
where  olfactory  stimuli  are  combined  with  other  sensory 
impressions,  each  nucleus  having  its  own  particular  reflex 
pattern.  The  intermediate  nucleus  (also  called  tuberculum 
olfactorium  and  by  Edinger  lobus  parolfactorius)  is  better 
developed  in  many  other  mammals  than  in  man,   and  is 


TITE    OLFACTORY    APPARATUS  24') 

probably  especially  concerned  with  the  feeding  reflexes  of  the 
snout  or  muzzle,  including  smell,  touch,  taste,  and  musculai' 
sensibility,  a  physiological  complex  which  Edinger  has  called 
collectively  the  "oral  sense."  This  complex  of  muzzle  reflexes 
has  probably  played  a  very  important  role  in  the  earlier  stages 
of  the  evolutionary  history  of  the  correlation  centers  of  the 
cerebral  hemispheres  (see  the  works  by  Edinger  cited  at  the 
end  of  this  chapter). 

From  these  nuclei  of  the  olfactory  area  fiber  tracts  of  the 
third  order  pass  to  the  mammillary  bodies  of  the  hypothalamus 
and  to  the  habenular  bodies  of  the  epithalamus,  from  both  of 
which,  after  another  synapse,  tracts  lead  downward  into  the 
motor  centers  of  the  midbrain  in  the  cerebral  peduncle.  The 
path  from  the  mammillary  body  is  the  tractus  mamillo-pedun- 
cularis  (Figs.  75,  78,  106).  The  path  from  the  habenular  body 
is  the  tractus  habenulo-peduncularis  (fasciculus  retroflexus, 
B.  N.  A.,  or  Meynert's  bundle,  Fig.  106).  The  mammillary 
body  also  sends  a  tract  into  the  anterior  nucleus  of  the  thala- 
mus, the  tractus  mamillo-thalamicus  (fasciculus  thalamo- 
mamillaris,  B.  N.  A.,  or  tract  of  Vicq  d'Azyr,  Figs.  78,  106), 
for  the  correlation  of  olfactory  with  general  somatic  reactions. 
There  is  also  a  direct  path  between  the  secondary  olfactory 
area  and  the  cerebral  peduncle,  without  connection  with  the 
diencephalon,  by  Avay  of  the  tractus  olfacto-tegmentalis 
(Fig.  106).  In  the  epithalamus  the  olfactory  nervous  im- 
pulses are  correlated  with  those  of  the  somatic  sensory  centers 
of  the  thalamus,  especially  the  optic  and  tactual  systems 
(p.  1 77) ;  in  the  hypothalamus  they  are  correlated  with  gus- 
tatory and  various  visceral  sensory  systems  (p.  179). 

The  preceding  account  includes  a  description  of  a  few  of  the 
more  important  pathways  involved  in  olfactory  reflexes.  Ol- 
factory impulses  which  reach  the  cerebral  cortex  take  a  differ- 
ent path.  They  are  carried  from  all  parts  of  the  secondary 
olfactory  area  at  the  base  of  the  olfactory  bulb  into  the  hippo- 
campus (which  composes  the  greater  part  of  the  archipallium 
in  the  human  brain)  by  several  olfacto-cortical  tracts,  whose 
courses  in  the  human  brain  are  so  tortuous  that  we  shall  not 
attempt  to  describe  them  here. 

The  hippocampus   (formerly  called  the  Amnion's  horn  or 


246  INTRODUCTION  TO  NEUROLOGY 

cornu  Ammonis,  also  the  hippocampus  major,  Fig.  107)  is  a 
special  convolution  which  forms  the  postero-ventral  border 
of  the  cerebral  cortex;  it  is  rolled  into  the  posterior  horn  of  the 
lateral  ventricle  so  that  it  does  not  appear  on  the  surface  of  the 
brain.     It  is   connect-ed   with   the   remainder   of  the   cortex 


Fig.   107. — Section   across   the   hippocampus   and   gyrus   hippocampi   of   the 
human  brain.      (After  Edinger.) 


(neopallium)  by  cortex  of  transitional  type,  the  hippocampal 
gyrus  (gyrus  hippocampi),  from  which  it  is  separated  by  a 
deep  groove,  the  fissura  hippocampi.  The  free  border  of  the 
hippocampus  is  accompanied  for  its  entire  length  by  a  strong 
band  of  fibers,  the  fimbria,  through  which  olfactory  projection 
fibers   enter  it  from   the   secondary   olfactory    area.     These 


THE  OLFACTORY  APPARATUS  247 

fibers  discharge  into  a  subsidiary  part  of  the  hippocampus, 
the  dentate  gyrus  (gyrus  dentatus,  also  called  fascia  dentata), 
at  a,  Fig.  107. 

The  hippocampus  is  connected  with  all  other  parts  of  the 
cerebral  cortex  by  an  extensive  system  of  association  tracts 
forming  the  alveus  (Fig.  107),  thus  providing  for  those  complex 
interactions  of  diverse  functional  systems  for  which  the  cortex 
is  especially  adapted.  There  is  also  an  efferent  pathway  from 
the  hippocampus  to  the  brain  stem  through  the  fimbria  and  the 
column  of  the  fornix  (Figs.  78,  106,  107),  whose  fibers  termi- 
nate in  both  the  hypothalamus  and  the  epithalamus.  Having 
reached  the  hypothalamus  and  epithalamus,  these  motor 
impulses  of  cortical  origin  are  conveyed  to  the  motor  centers 
in  the  midbrain  by  the  same  pathways  as  are  the  reflex 
impulses  already  described. 

'  Summary. — The  olfactory  centers  (rhinencephalon)  make  up 
nearly  the  entire  forebrain  in  fishes,  and  in  higher  vertebrates 
progressively  more  non-olfactory  centers  are  added  to  this  part 
of  the  brain.  The  non-olfactory  parts  of  the  cerebral  hemi- 
sphere comprise  chiefly  the  corpus  striatum  and  the  neopallium ; 
the  latter  makes  up  by  far  the  larger  part  of  the  human  hemi- 
sphere. The  rhinencephalon  consists  of  a  reflex  part  in  the 
brain  stem  and  a  cortical  part  in  the  archipallium.  Smell  and 
taste  are  both  chemically  excited  senses,  but  the  threshold  of 
excitation  is  much  lower  in  the  case  of  smell.  This  is  brought 
about  by  the  suppression  of  a  synapse  in  the  peripheral  receptor 
organ  and  by  a  complex  mechanism  for  the  summation  and 
reinforcement  of  stimuli  in  the  primary  olfactory  center  in  the 
olfactory  bulb.  The  secondary  olfactory  center  is  the  olfac- 
tory area,  which  has  three  parts,  each  of  which  is  a  reflex 
center  of  distinctive  type.  The  reflex  path  from  the  secondary 
center  passes  backward  to  the  epithalamus  and  to  the  hypo- 
thalamus, from  both  of  which  a  descending  path  goes  to  the 
motor  centers  in  the  cerebral  peduncle.  The  secondary 
olfactory  center  also  discharges  into  the  olfactory  cerebral 
cortex,  which  is  chiefly  contained  within  the  hippocampus  and 
from  which  manifold  association  pathways  connect  with  all 
other  parts  of  the  cerebral  cortex. 


248  INTRODUCTION    TO    NEUROLOGY 


Liter AT UKE 

On  the  olfactory  centers  of  lower  vertebrates,  see  also  the  papers  by 
Crosby,  Herrick,  Johnston  and  Sheldon  cited  at  the  end  of  Chapters 
IX  and  X. 

Barker,  L.  F.     1901.     The  Nervous  System,  New  York,  pp.  747-781. 

Brookover,  C.  1914.  The  Nervus  Terminalis  in  Adult  Man,  Jour. 
Comp.  Neurology,  vol.  xxiv,  pp.  131-135. 

— .  1917.  The  Peripheral  Distribution  of  the  Nervus  Terminalis  in  an 
Infant,  Ibid.,  vol.  xxvii. 

Edinger,  L.  1908.  Vorlesungen  iiber  den  Bau  der  nervosen  Zentral- 
organe,  Bd.  2,  Vergleichende  Anatomie  des  Gehirns,  Leipzig. 

— .  1908.  The  Relations  of  Comparative  Anatomy  to  Comparative 
Psychology,  Jour.  Comp.  Neurology,  vol.  xviii,  pp.  437-457. 

— .  1908.  Ueber  die  Oralsinne  dienenden  Apparate  am  Gehirn  der 
Sanger,  Deutsch.  Zeits.  f.  Nervenheilkunde,  Bd.  36. 

Herrick,  C.  Judson.  1908.  On  the  Phylogenetic  Differentiation  of 
the  Organs  of  Smell  and  Taste,  Jour.  Comp.  Neurology,  vol.  xviii,  pp. 
157-166. 

— .  1910.  The  Evolution  of  Intelligence  and  Its  Organs,  Science, 
N.  S.,  vol.  xxxi,  pp.  7-18. 

HuBER,  G.  Carl  and  Guild,  S.  R.  1913.  Observations  on  the  Pe- 
ripheral Distribution  of  the  Nervus  Terminalis  in  Mammalia,  Anat. 
Record,  vol.  vii,  pp.  253-272. 

Johnston,  J.  B.  1906.  The  Nervous  System  of  Vertebrates,  Phila- 
delphia, pp.  176-189,  292-337. 

• — .  1913.  Nervus  Terminahs  in  Reptiles  and  Mammals,  Jour. 
Comp.  NeuroIog3^,  vol.  xxiii,  pp.  97-120. 

— .  1914.  The  Nervus  Terminalis  in  Man  and  Mammals,  Anat. 
Record,  vol.  viii,  pp.  185-198. 

Kappers,  C.  U.  a.  1908.  Die  Phylogenese  des  Rhinencephalons,  des 
Corpus  Striatum  und  der  Vorderhirnkommissuren,  Folia  Neurobiologica, 
Bd.  1,  pp.  173-288. 

McCoTTER,  R.  E.  1912.  The  Connections  of  the  Vomeronasal 
Nerves  with  the  Accessory  Olfactory  Bulb  in  the  Opossum  and  Other 
Mammals,  Anat.  Record,  vol.  vi,  pp.  299-318. 

— .  1913.  The  Nervus  Terminalis  in  the  Adult  Dog  and  Cat,  Jour. 
Comp.  Neurology,  vol.  xxiii,  pp.  145-152. 

— .  1917.  The  Vomeronasal  Apparatus  in  Chrysemys  punctata  and 
Rana  catesbiana,  Anat.  Record,  vol.  xiii,  pp.  51-67. 

ZwAARDEMAKER,  H.     1985.     Die  Physiologic  des  Geruchs,  Leipzig. 

— .     1900.     Revue  generale  sur  I'olfaction,  Ann6e  Psychol.,  vol.  vi. 

— .     1902.     Geruch.     Ergebnisse  der  Physiologic,  Bd.  1. 


CHAPTER  XVI 
THE  SYMPATHETIC  NERVOUS  SYSTEM 

Before  we  can  extend  our  analysis  of  the  conduction  paths 
into  the  reahn  of  the  visceral  activities  of  the  body  we  must  con- 
sider briefly  the  sympathetic  nervous  system  through  which  the 
regulatory  control  of  these  activities  is  effected.  Most  of  the 
visceral  activities  are  performed  either  unconsciously  or  with 
very  imperfect  awareness.  The  nervous  mechanisms  of  manj^ 
of  them  are  still  obscure.  Nevertheless  the  visceral  functions 
as  a  whole  are  of  enormous  importance,  not  oiily  in  the  mainte- 
nance of  the  physical  welfare  of  the  body,  but  also  as  the 
organic  backgiMDund  of  the  entire  conscious  life  (see  p.  288). 

Many  of  the  visceral  functions  can  be  performed  quite  apart 
from  any  nervous  control  whatever  by  the  intrinsic  mechan- 
isms of  the  viscera  themselves.  The  heart  musculature,  for 
instance,  beats  automatically  with  a  characteristic  rhyt^hm,  and 
most  of  the  other  visceral  muscles  have  the  power  of  auto- 
matic rhythmic  contraction.  Some  of  the  glands  of  the  bodj^ 
may  be  excited  to  secretion  by  chemical  substances  dissolved 
in  the  blood.  For  instance,  when  food  enters  the  small  intes- 
tine from  the  stomach,  the  intestinal  glands  are  directly  excited 
to  activity  by  the  presence  of  the  food.  Some  of  their  secre- 
tions are  poured  out  into  the  intestine  to  act  as  digestive 
juices;  others  are  absorbed  directly  by  the  blood  (internal 
secretions  or  hormones).  Among  the  latter  is  secretin,  a 
substance  which  is  carried  by  the  blood-stream  to  the  pancreas 
and  there  excites  the  secretory  activity  of  this  organ  to 
the  formation  of  pancreatic  juice,  which  is,  in  turn,  poured  into 
the  intestine.  The  very  complex  secretory  activities  involved 
in  the  formation  of  the  intestinal  and  pancreatic  juices  under 
the  stimulus  offered  by  the  presence  of  food  in  the  intestine, 
therefore,  are  not  directly  excited  by  the  nervous  system, 
though  they  may  be  brought  under  nervous  control  in  a 

249 


250  INTRODUCTION   TO    NEUROLOGY 

secondary  way.  And,  as  a  matter  of  fact,  in  all  of  these 
visceral  functions  the  non-nervous  and  the  nervous  functions 
actually  cooperate  in  most  intimate  fashion. 

Most  of  the  viscera  are,  accordingly,  under  immediate 
nervous  control  of  two  sorts.  This  control  is  partly  derived 
from  the  ganglia  of  the  sympathetic  nervous  system  which  are 
distributed  widely  throughout  the  body,  and  partly  from  the 
central  nervous  system.  The  nervous  impulses  involved  in 
the  second  type  of  control  are,  moreover,  always  distributed 
to  the  viscera  through  the  sympathetic  system. 

A  clear  analytic  description  of  the  visceral  nervous  systems  is 
extremely  difficult,  and  there  is  wide  diversity  of  usage,  not 
only  in  the  terminology  employed  in  these  descriptions,  but 
also  in  the  fundamental  concepts  upon  which  they  are  based. 
The  brain  and  spinal  cord  and  the  cranial  and  spinal  nerves 
and  their  end-organs  in  the  aggregate  constitute  the  cerebro- 
spinal nervous  system.  The  cell  bodies  of  the  neurons  of  this 
system  all  lie  within  the  spinal  cord  and  brain  (including  the 
retina)  or  in  the  ganglia  on  the  sensory  roots  of  the  cranial 
and  spinal  nerves.  There  are,  however  innumerable  other 
ganglia  distributed  very  widely  throughout  the  body,  which 
are  connected  with  each  other  and  with  the  central  nervous 
system  by  intricate  nervous  plexuses.  These  constitute 
the  sympathetic  ganglia  and  nerves,  or  in  the  aggregate  the 
sympathetic  nervous  system. 

There  is  an  especially  important  group  of  sympathetic 
ganglia  which  are  arranged  in  two  longitudinal  series  extending 
one  on  each  side  of  the  vertebral  column.  These  ganglia 
constitute  the  vertebral  sympathetic  trunks  or  chains,  and 
throughout  the  middle  part  of  the  body  there  is  one  ganglion 
of  each  trunk  for  each  spinal  root  (Fig.  41,  p.  115).  Communi- 
cating branches  connect  the  ganglia  of  the  trunks  with  their 
respective  spinal  roots,  and  from  these  ganglia  sympathetic 
nerves  extend  out  peripherally  to  ramify  among  the  viscera 
and  other  tissues  of  the  body.  Ganglion  cells  are  scattered 
among  these  peripheral  sympathetic  nerves,  and  in  some  places, 
especially  among  the  abdominal  viscera,  these  cells  are  crowded 
together  to  form  large  ganglionic  plexuses  (Fig.  108). 

When  further  analyzed,  the  sympathetic  nervous  system  is 


THE    SYMPATHETIC    NERVOUS    SYSTEM 


251 


Mnxillrirv  norve 


(  ili.ir.v  caiiclion 
Sphenopalatine  ganglion 
Superior  cervical  ganglion  of  sympathetic 


Cervical  plexus 


Brachial  plexus 


Greater  splanchnic  ner\  e 
Lesser  splanchnic  nerve 


Lumbar  plexus 


Sacral  plexu; 


Pharyngeal  plexus 

Middle  cervical  ganglion  of 

sympathetic 
Inferior  cervical  g.  of  sympathetic 
Recurrent  nerve 

—Bronchial  plexus 

Cardiac  plexus 

Esophageal  plexus 
■Coronary  plexus 


Left  vagus  ners'S 

.Gastric  plexus 
Celiac  plexus 

Superior  mesenteric  plexua 


Aortic  plexus 

Inferior  mesenteric  plexua 

Hypogastric  plexus 

Pelvic  plexus 

Bladder 
Vesical  plexus 


Fig.  108. — The  sympathetic  nervous  system,  ithistrating  the  right  sym- 
pathetic trunk  and  its  relation  with  the  spinal  nerves  and  with  the  peripheral 
sympathetic  ganglionated  plexuses;  cf.  Fig.  41,  p.  115.     (After  Schwalhe.) 


252  INTBODtrCTION   TO    NEUROLOGY 

found  to  consist  of  two  imperfectly  separable  parts.  The  first 
is  a  diffusely  arranged  peripheral  plexus  of  nerve-cells  and  fibers 
adapted  for  the  local  control  of  the  organs  with  which  it  is  con- 
nected. This  we  shall  call  the  peripheral  autonomous  part  of 
the  sympathetic  system  (this  is  not  the  same  as  the  autonomic 
nervous  system  of  Langley,  see  p.  258).  The  second  part  of 
the  sympathetic  system  includes  those  neurons  which  put 
the  peripheral  autonomous  system  into  functional  connection 
with  the  central  nervous  system,  thus  providing  a  central 
regulatory  control  over  the  autonomous  system.  This  part 
of  the  sympathetic  nervous  system  includes  the  peripheral 
courses  of  the  neurons  involved  in  the  general  cerebrospinal 
visceral  reflex  systems  (see  pp.  81,  94,  98). 

The  peripheral  autonomous  nervous  system  appears  to  be  a 
direct  survival  of  that  diffuse  type  of  nervous  system  which 
alone  is  found  in  the  lowest  animals  which  possess  nerves  at 
all,  such  as  some  jelly-fishes  and  worms.  It  serves  to  supple- 
ment the  non-nervous  protoplasmic  activities  of  the  different 
tissues  which  cooperate  in  the  performance  of  the  work  of  the 
several  organs.  With  increasing  complexity  of  the  organi- 
zation of  the  body  during  evolution,  protoplasmic  activities 
on  the  lower  physiological  level  are  no  longer  adequate  to 
effect  the  integration  and  coordination  of  the  more  diversified 
functions  to  be  performed  in  these  complex  organs.  This 
type  of  local  control  is  then  effected  by  the  peripheral  auto- 
nomous nervous  system. 

The  central  nervous  system  of  higher  animals  is  supposed 
to  have  developed  by  a  concentration  of  ganglia  in  such  a 
diffuse  system  (see  p.  28),  a  portion  of  which  remains  as  the 
peripheral  autonomous  sympathetic  system  (Fig.  17,  p.  56). 
But  during  further  evolution  the  central  nervous  system 
increased  in  importance  for  integrating  and  regulating  the 
functions  of  the  body,  the  central  control  of  the  viscera  as- 
sumed greater  importance,  and  the  general  cerebro-spinal 
visceral  systems  were  developed  to  serve  this  function. 

That  the  neurons  of  the  peripheral  autonomous  system 
are  of  more  generahzed  type  (and  therefore  probably  more 
primitive)  than  are  other  types  of  neurons  is  suggested  by  the 
fact  that  they  survive  experimental  total  anemia  much  longer 


THE    SYMPATHETIC    NERVOUS    SYSTEM  253 

than  do  any  other  neurons.  Cannon  and  Burket  (1913) 
pomt  out  that  neurons  of  the  myenteric  plexus  (p.  268) 
may  survive  the  anemia  cause^;!  by  Hgature  of  the  blood  vessels 
for  as  much  as  G  or  7  hours.  Neurons  of  the  ganglia  of  the 
sympathetic  trunk  (cerebro-spinal  visceral  system)  cannot 
survive  more  than  one  hour  of  this  treatment,  and  those  of 
the  spinal  cord  less  than  this  time,  while  those  of  the  brain 
cannot  survive  more  than  15  or  20  minutes. 

Figures  56  (p.  137)  illustrates  the  typical  arrangement  of  the 
visceral  sensory  and  motor  fibers  in  the  spinal  nerves,  and  their 
relations  to  the  sjanpathetic  ganglia  and  nerves.  These  fibers, 
of  course,  belong  to  the  cerebro-spinal  visceral  systems;  the 
peripheral  autonomous  system  is  not  included  in  the  diagram. 
The  central  control  of  the  visceral  apparatus  is  effected  (1)  by 
afferent  visceral  nerve-fibers  distributed  peripherally  through 
the  sympathetic  nerves  and  entering  the  spinal  cord  through 
the  dorsal  spinal  roots,  and  (2)  by  efferent  visceral  nerves 
which  leave  the  spinal  cord  through  the  ventral  roots  and  also 
enter  the  sympathetic  nerves.  In  lower  vertebrates  (and 
possibly  also  in  man)  some  of  these  fibers  leave  by  the  dorsal 
roots  also. 

The  cell  bodies  of  the  afferent  neurons  he  in  part  in  the 
spinal  ganglia  and  in  part  in  the  sympathetic  gangHa.  Figure 
109  illustrates  the  connections  of  these  two  types  of  afferent 
visceral  neurons.  Neuron  3  of  this  figure  may  transmit  its 
impulse  either  directly  into  the  spinal  cord  through  its  centrally 
directed  process  or  by  a  collateral  branch  to  some  other  cell 
body  of  the  spinal  ganghon  (neuron  1).  The  fiber  marked  4 
arises  from  a  cell-body  lying  in  some  sympathetic  ganglion  and 
terminates  in  synaptic  relation  with  some  neuron  whose  cell 
body  lies  in  the  spinal  ganghon,  which,  in  turn,  may  transmit 
this  visceral  impulse  into  the  spinal  cord  in  addition  to  its 
own  proper  function,  say,  of  cutaneous  sensibihty. 

The  relations  just  described  probably  provide  the  neurolog- 
ical mechanism  of  some  of  the  curious  phenomena  known  as 
referred  pains.  It  is  well  known  that  disease  of  certain  inter- 
nal organs  may  be  accompanied  by  no  pain  at  the  site  of  the 
injury,  but  by  cutaneous  pain  and  tenderness  in  remote  parts 
of  the  body.     Fig.  1 10  illustrates  some  of  these  areas  of  referred 


254 


INTRODUCTION   TO    NEUROLOGY 


pain  and  the  sources  of  the  excitations.  The  mechanisms 
shown  in  Fig.  109  show  how  an  inflammatory  process  or  other 
injury  of  the  sympathetic  nerves  associated  with  these  deep 
viscera  may  readily  be  carried  over  to  the  related  neurons  of 
the   somatic  sensory  system.     Many  referred  pains  are  un- 


dorsal  root 


spinal  ganglion 


peripheral 
nerve 


Fig.  109. — Diagram  illustrating  three  ways  in  which  afferent  visceral 
fibers  may  connect  with  the  central  nervous  system  through  the  spinal 
ganglia  (cf.  Fig.  56,  p.  137).  Neurons  1  and  2  are  typical  somatic  sensory 
neurons,  whose  peripheral  fibers  reach  the  skin.  Neuron  3  is  a  visceral 
sensory  neuron,  whose  peripheral  fiber  enters  the  sympathetic  nervous  sys- 
tem through  the  communicating  branch  (this  neuron  is  drawn  in  fine  dotted 
lines  in  Fig.  56).  Neurons  of  the  third  type  maj^  bring  in  afferent  impulses 
from  the  viscera  through,  their  peripheral  processes  and  transmit  these  im- 
pulses directly  to  the  spinal  cord  through  their  central  processes.  A  col- 
lateral branch  from  this  neuron,  moreover,  may  carry  the  visceral  impulse 
to  the  cell  body  of  a  neuron  of  type  1,  which  thus  serves  to  convey  both 
somatic  impulses  from  the  skin  and  visceral  impulses  from  some  deep-seated 
organ.  The  spinal  ganglion  also  receives  nerve-fibers  of  the  type  marked  4, 
whose  cell  bodies  lie  in  the  sympathetic  ganglia.  These  probably  convey 
visceral  afferent  impulses  as  far  as  the  spinal  ganglion,  which  are  then  trans- 
mitted to  the  spinal  cord  through  a  somatic  sensory  neuron.  These  arrange- 
ments are  described  in  detail  l>v  Dogiel. 


doubtedly  due  to  similar  collocations  of  visceral  and  somatic 
sensory  paths  within  the  spinal  cord  and  brain.  Since  the 
functions  of  these  visceral  nerves  do  not  usually  come  into 
consciousness  at  all,  the  pain  will  be  referred  to  the  peripheral 


THE    SYMPATHETIC    NERVOT'S    SYSTEM 


255 


Ancemia 

KndftTnetritit 
Bladder? 


Neurimtlunia 
{apinal  irritation) 

Splenitis l""~l~" 


Z-'f\.JyDteay»d  tetih 
-lu'  ,^Pharj/nffi(ia 

'  Otitis  media 


Fig.   110. — The  locations  of  referred  pains  and  their  causes, 
from  Starr's  Nervous  Diseases.) 


(After  Dana, 


Area,  cerebrospinal 

nerves. 

I.  Trigeminus,    fa- 
cial. 
II.  Upper  cervical. 

III.  Lower  four  cer- 

vical   and    first 
thoracic. 

IV.  Upper  six  thor- 

acic. 
V.  Lower  six  thor- 


VI.  Twelfth   thoracic 

and  fourth  lum- 
bar. 

VII.  Fifth  lumbar  and 

five  sacral. 


Distribution. 
Face  and  anterior 

scalp. 
Occiput,  neck. 
Upper  extremity. 


Thorax. 

Abdomen,  upper 
lumbar. 

Lumbar,  upper 
gluteal,  anterior 
thigh,  and  knee. 

Lower  gluteal, 
posterior  thigh 
and  leg. 


Associated  ganglia 
of  sympathetic. 

Four  cerebral. 

First  cervical. 
Second  and  third 

cervical,     first 

thoracic. 
First     to  5  sixth 

thoracic. 
Sixth  to  twelfth 

thoracic. 

First      to      fifth 
lumbar. 

First      to      fifth 
sacral. 


Distribution. 
Head. 

Head,  ear. 
Heart. 


Lungs. 

Viscera  of  ab- 
domen and 
testes. 

Pelvic  or- 
gans. 


Pelvic 
gans 
legs. 


and 


256  INTRODUCTION  TO  NEUROLOGY 

area  of  distribution  of  the  associated  somatic  nerve,  which  has 
a  distinct   'local  sign,"  or  habitual  peripheral  reference. 

The  efferent  fibers  of  the  cerebro-spinal  visceral  system  arise 
from  several  groups  of  cells  in  the  intermediate  zone  between 
the  dorsal  and  ventral  'gray  columns  of  the  spinal  cord,  and  in 
particular  from  an  intermedio-lateral  column  of  cells  at  the 
margin  of  the  lateral  column  of  gray  matter  (Fig.  56,  p.  137). 
These  efferent  fibers  never  reach  their  peripheral  terminations 
directly.  They  always  end  in  some  sympathetic  ganglion, 
either  of  the  vertebral  ganglionic  trunk  or  one  of  the  peripheral 
sympathetic  ganglia.  Here  there  is  a  synapse,  and  a  second 
neuron  of  the  sympathetic  ganglion  in  question  takes  up  the 
nervous  impulse  and  transmits  it  to  its  termination  in  some 
unstriated  visceral  muscle  or  gland.  The  efferent  fiber  arising 
from  a  cell  body  within  the  spinal  cord  is  termed  the  pre- 
ganglionic fiber,  and  the  peripheral  fiber  arising  from  a  neuron 
of  the  sympathetic  ganglion  is  the  'postganglionic  fiber.  The 
former  is  usually  a  small  myelinated  fiber;  the  latter  is  usually 
unmyelinated.  The  preceding  description  is  applicable  to 
the  visceral  nervous  system  in  the  trunk  region  of  the  body. 
In  the  head  the  connections  of  the  nerves  of  this  type  are 
much  more  complex. 

Langley  and  others  have  shown  that  what  is  here  termed  the 
general  cerebro-spinal  visceral  system  is  related  to  four  distinct 
regions  of  the  central  nervous  system,  as  illustrated  by  Fig. 
111.  The  portions  of  the  sympathetic  system  related  to  these 
respective  regions  are  as  follows;  (1)  The  midbrain  sympa- 
thetic, comprising  chiefly  the  ciliary  ganglion  behind  the  eye. 
and  its  nerves,  these  being  related  to  the  brain  through  the 
III  cranial  nerve.  (2)  The  bulbar  sympathetic,  related  to 
the  brain  chiefly  through  the  VII,  IX,  and  X  cranial  nerves. 
(3)  The  thoracic-lumbar  sympathetic,  related  to  the  spinal 
cord  through  the  I  thoracic  to  II  or  III  lumbar  nerves.  (4) 
The  sacral  sympathetic,  related  to  the  spinal  cord  through  the 
II  to  IV  sacral  nerves. 

Each  of  these  four  regions  has  its  own  distinctive  physiolog- 
ical characteristics,  including  in  some  cases  a  special  type  of 
reaction  to  certain  drugs.  They  all  exhibit  a  common  reaction 
to  nicotin  in  physiological  doses.     The  effect  of  this  poison 


THE    SYMPATHETir    NERVOUS    SYSTEM 


257 


Sphincter  of  iris  "I 
Ciliary  muscle  J 

Heart,  blood-vessels  of  mucous  mem- 
branes of  head,  salivary  glands,  wails  of 
digestive  tract  from  mouth  to  descending 
colon,  including  outgrowths  of  this  re- 
gion— trachea  and,  lungs,  gastric  glands, 
liver,  pancreas. 


and,  lungs,   gas 


Dilator  of  iris,  orbital  muscles,  arteries,  1 
muscles  and  glands  of  the  skin,  blood- 
vessels of  lungs  and  abdominal  viscera  and  | 
of  digestive  tract  between  mouth  and  rec-  j- 
turn,  arteries  of  skeletal  muscles,  muscles  I 
of  spleen,  ureter,  and  internal  generative  1 
organs.  J 


Arteries  of  rectum,  anus,  and  external  i 
generative  organs,  muscles  of  external  gen-  ( 
erative  organs,  walls  of  bladder  and  , 
urethra,  walls  of  descending  colon  to  anus.  J 


Midbrain  sympathetic 


Bulbar  sympathetic 


/Thoracic-lumbar  sjTnpathetic 
1 1  thoracic  to  II  or  III  lumbar 


f  Sacral  sj-mpathetic 
ill  to  IV  sacral 


Fig.    111.- 


-Diagram  of  the  central  localization  of  the  cerebro-spinal  visceral 
nervous  connections.     (Modified  from  Langley.) 


17 


258  INTRODUCTION    TO    NEUROLOGY 

is  to  paralyze  the  synapses  between  the  pregangHonic  and  the 
postgangHonic  neurons  and  thus  to  isolate  the  peripheral 
sympathetic  neurons  physiologically  from  efferent  impulses 
arising  within  the  central  nervous  system.  Adrenalin  (extract 
of  the  suprarenal  glands)  affects  chiefly  the  thoracic-lumbar 
sympathetic  system  (see  p.  283).  On  the  other  hand,  poisons 
of  a  different  group,  including  atropin,  muscarin;  and  pilo- 
carpin,  are  said  to  act  chiefly  upon  the  midbrain,  bulbar  and 
sacral  sympathetic,  but  not  upon  the  thoracic-lumbar  system. 
There  are  other  cases  of  very  specific  action  of  drugs  upon 
special  parts  of  the  sympathetic  nervous  system. 

The  analysis  of  the  sympathetic  nervous  system  given  above  differs 
in  some  respects  from  any  other  in  common  use.  But  there  is  no  uni- 
formity in  current  usage  (for  a  summarj'  of  the  variations  in  the  nomen- 
clature of  the  visceral  nervous  system  see  Ranson,  1917). 

The  simplest  procedure  seems  to  be  to  retain  the  older  usage  and  em- 
ploy the  word  sympathetic  system  as  a  purely  topographic  name  for  that 
portion  of  the  visceral  nervous  system  which  can  be  dissected  away 
from  the  cerebro-spinal  nerves,  viz.,  the  ganglionated  trunks  and  plex- 
uses, together  with  the  whole  of  what  is  here  termed  the  peripheral 
autonom.ous  visceral  system,  and  their  related  peripheral  nerves.  The 
rami  communicantes  provide  the  only  connection  between  this  system 
and  the  spinal  cord  and  spinal  nerves;  but  the  relations  of  the  sympathetic 
system  to  the  cranial  nerves  is  much  more  complex  and  the  anatomical 
separation  of  these  two  systems  here  is  often  impossible. 

There  is  a  practical  justification  in  dissecting-room  convenience  for 
this  usage;  but  for  purposes  of  finer  histological  and  physiological  analysis 
the  distinction  between  sympathetic  and  cerebrospinal  nerves  here 
drawn  must  be  ignored.  The  term  autonomic  nervous  sj^stem  has  been 
used  in  so  diverse  senses  that  it  should  be  abandoned  altogether.! 

Langley  calls  the  entire  sympathetic  system  the  autonomic  system,  and 
limits  the  application  of  the  term  "sj^mpathetic  "  to  what  is  here  called  the 
thoracic-lumbar  sympathetic.  There  is  no  adequate  ground  for  his  belief 
that  the  latter  is  genetically  different  from  the  other  parts  of  the  cerebro- 
spinal visceral  apparatus,  though  its  physiological  characteristics  are  very 
distinctive.  Many  of  the  viscera  have  a  double  innervation  through  the 
sympathetic,  one  set  of  fibers  coming  from  the  midbrain,  bulbar,  or  sacral 
sympathetic  ganglia  and  an  antagonistic  set  coming  from  the  thoracic- 
lumbar  sympathetic  ganglia. 

Summary. — From  the  preceding  considerations  it  is  evident 
that  the  sympathetic  nervous  system  cannot  be  sharply  sepa- 
rated anatomically  or  physiologically  from  the  cerebro-spinal 
system.  The  cell  bodies  of  the  neurons  of  the  cerebro-spinal 
visceral  system  lie  partly  within  and  partly  without  the  central 


THE    SYMPATHETIC    NERVOUS    SYSTEM  259 

nervous  axis.  A  ganglionic  sympathetic  trunk  extends  on  each 
side  of  the  body  along  the  spinal  column,  and  the  ganglia  of  this 
trunk  are  connected  with  most  of  the  spinal  nerves  by  com- 
municating branches.  The  neurons  of  this  trunk  of  vertebral 
sympathetic  ganglia  belong  chiefly  to  the  cerebro-spinal  visceral 
system,  since  they  are  concerned  with  the  central  regulatory 
mechanism  of  the  viscera.  All  parts  of  the  visceral  nervous 
system  which  lie  peripherally  of  the  communicating  branches 
between  the  sympathetic  ganglicmated  trunks  and  the  spinal 
roots,  and  can  be  anatomically  separated  from  the  peripheral 
branches  of  the  cerebro-spinal  nerves,  are  commonly  described 
as  constituting  the  sympathetic  nervous  system.  This  system 
includes  the  ganglionated  trunks  bordering  the  spinal  column, 
to  which  reference  has  just  been  made,  the  larger  peripheral 
ganglionated  plexuses  of  the  head,  thorax,  and  abdomen,  and  a 
very  large  number  of  minute  sympathetic  ganglia  scattered 
everywhere  throughout  the  body.  This  sympathetic  nervous 
system  we  have  regarded  as  composed  of  two  imperfectly 
separable  parts:  (1)  a  series  of  autonomous  peripheral  ganglia 
for  the  local  regulation  of  the  organs  within  which  they  are 
found;  (2)  the  neurons  of  the  cerebro-spinal  visceral  systems 
which  enable  the  central  nervous  system  to  maintain  a  regula- 
tory control  over  the  intrinsic  autonomous  systems. 

Literature 

Cannon,  W.  B.  and  Burket,  I.  R.  1913.  The  Endurance  of  Anemia 
by  Nerve  Cells  in  the  Myenteric  Plexus,  Am.  Jour.  Physiol.,  vol.  xxxii, 
pp.  247-357. 

DoGiEL,  A.  S.  1908.  Der  Bau  der  Spinalganglien  des  Menschen  und 
der  Saugetiere,  Jena,  G.  Fischer,  1.51  pp.,  14  plates. 

Head,  H.  1893.  On  Disturbances  of  Sensation  with  Especial  Refer- 
ence to  the  Pain  of  Visceral  Disease,  Brain,  vol.  xvi,  pp.  1-133.- 

— .     1901.     The  Gulstonian  Lectures  for  1901,  Brain,  vol.  xxiv,  p.  398. 

Head  and  Campbell.  1901.  Pathology  of  Herpes  Zoster,  Brain,  vol. 
x.xiii,  p.  353. 

HuBER,  G.  C.  1897.  Lectures  on  the  Sympathetic  Nervous  System, 
.Jour.  Comp.  Neur.,  vol.  vii,  pp.  73-145. 

KuNTZ,  A.  1911.  The  Evolution  of  the  Sympathetic  Nervous  System 
in  Vertebrates,  Jour.  Comp.  Neur.,  vol.  xxi,  pp.  215-236. 

Langley,  J.  N.  1900.  The  Sympathetic  and  Other  Related  System.s 
of  Nerves,  in  Schaefer's  Text-book  of  Physiology,  London,  pp.  616-696. 

— .  1900.  On  .\xon-reflexes  in  the  Preganglionic  Fibers,  Jour,  of 
Physiol.,  vol.  xxv,  p.  364. 


260  INTRODUCTION    TO    NEUROLOGY 

Langley,  J.  N.  1903.  The  Autonomic  Nervous  System,  Brain,  vol. 
xxvi,  pp.  1-26. 

Onuf,  B.,  and  Collins,  J.  1900.  Experimental  Researches  on  the 
Central  Localization  of  the  Sympathetic  with  a  Critical  Review  of  its 
Anatomv  and  Physiology,  Archives  of  Neurology  and  Psychopathologv, 
vol.  iii,  p.  1-252. 

Ranson,  S.  W.  1917.  On  the  Use  of  the  Word  "  Sympathetic "  in 
Anatomical  and  Physiological  Literature,  Anat.  Rec,  vol.  xi,  pp.  397-400. 


CHAPTER  XVII 
THE  VISCERAL  AND  GUSTATORY  APPARATUS 

OiJR  knowledge  of  the  functional  localization  within  the 
spinal  cord  of  the  general  visceral  reflex  centers  related  to  the 
spinal  nerves  is  still  rather  indefinite.  Most  of  the  cerebro- 
spinal control  of  the  visceral  reactions  of  the  body  is  effected 
from  the  bulbar  sympathetic  centers  by  way  of  the  vagus 
nerve.  The  afferent  fibers  of  these  systems  all  enter  the 
fasciculus  solitarius,  a  longitudinal  bundle  of  fibers  in  the 
lower  part  of  the  medulla  oblongata,  and  they  terminate  in 
the  nucleus  of  visceral  sensory  neurons  which  accompanies 
this  fasciculus  (Figs.  71-74,  77,  114).  The  special  visceral 
fibers  of  the  nerves  of  taste  also  terminate  in  this  nucleus. 
The  efferent  fibers  of  these  systems  arise  chiefly  from  the 
dorsal  motor  nucleus  of  the  vagus,  a  cluster  of  neurons  which 
produces  an  eminence  in  the  floor  of  the  fourth  ventricle  known 
as  the  ala  cinerea  or  trigonum  vagi  (Figs.  71-74,  114).  From 
this  nucleus  arise  preganglionic  fibers  for  the  innervation  of 
various  systems  of  visceral  muscles  of  blood-vessels,  esophagus, 
stomach,  intestine,  bronchi,  and  others. 

Most  viscera  possess  a  double  innervation — from  the  thora- 
cic-lumbar sympathetic  S3'^stem  and  from  the  midbrain,  bulbar, 
or  sacral  system  (see  p.  256).  For  instance,  the  heart-beat  is 
accelerated  by  the  thoracic-lumbar  sj^stem  and  inhibited  by 
the  bulbar  system  through  the  vagus;  and  the  iris  is  contracted 
through  the  midbrain  sympathetic,  but  dilated  through  the 
thoracic  by  waj^  of  the  superior  cervical  ganglion  (p.  235). 

Organs  of  Circulation. — The  nervous  control  of  the  heart 
and  blood-vessels  is  far  too  complex  for  full  description  here. 
A  few  general  features  only  can  be  touched  upon. 

The  rate  of  blood  flow  may  be  varied  for  the  body  as  a  whole 
by  changes  in  the  rate  and  force  of  the  pulsations  of  the  heart, 
and  for  particular  parts  of  the  body  by  changes  in  the  caliber 

261 


262  INTRODUCTION  TO  NEUROLOGY 

of  its  blood-vessels.  The  heart  beats  automatically,  but  its 
rate  is  regulated  through  the  cardiac  nerves.  The  caliber  of 
the  smaller  blood-vessels  and  hence  the  amount  of  blood  which 
can  pass  through  them  is  regulated  by  vasomotor  nerves. 
Both  the  heart  and  the  muscular  walls  of  the  vessels  have  a 
double  innervation.  The  heart  has  an  accelerator  nerve  and 
an  inhibitory  nerve;  the  smaller  arteries  have  vasodilator 
and  vasoconstrictor  nerves.  The  amount  of  blood  pumped 
by  the  heart  at  any  time  will  depend  upon  the  equilibrium 
existing  between  its  accelerator  and  its  inhibitory  fibers  and 
upon  the  resistance  offered  by  the  peripheral  vessels;  that 
flowing  through  any  particular  system  of  blood-vessels  will 
be  affected  also  by  the  equilibrium  between  the  vasodilator 
and  the  vasoconstrictor  nerves  of  these  vessels. 

There  are  sympathetic  ganglia  within  the  heart.  Its 
extrinsic  nerve  supply  includes  afferent  fibers  to  the  brain  and 
efferent  fibers  of  two  sorts,  viz.,  the  accelerator  and  inhibitory 
fibers  already  mentioned.  The  afferent  fibers  are  represented 
in  a  small  sympathetic  nerve,  the  nerve  of  Cyon,  which  is  also 
called  the  depressor  nerve.  They  arise  from  the  walls  of  the 
ventricles  of  the  heart  and  join  the  vagus  trunk,  through  which 
they  enter  the  medulla  oblongata.  Stimulation  of  this  nerve 
produces  a  fall  of  arterial  pressure  by  dilating  the  vessels 
throughout  the  body,  especially  in  the  viscera.  It  appears 
to  act  to  reduce  the  labor  of  the  heart  when  intraventricular 
pressure  becomes  excessive. 

The  medulla  oblongata  contains  a  center  whose  stimulation 
causes  inhibition  of  the  heart-beat.  These  efferent  fibers  go 
out  as  preganglionic  fibers  of  the  vagus  nerve  and  terminate  in 
the  cardiac  sympathetic  plexus  (Fig.  108),  where  their  post- 
ganglionic neurons  are  located.  There  is  also  a  center  in  the 
medulla  oblongata  (which  has  not  been  precisely  localized) 
whose  stimulation  causes  acceleration  of  the  heart-beat. 
These  accelerator  nerve-fibers  do  not  leave  the  brain  through 
the  vagus,  but  apparently  they  descend  through  the  spinal 
cord  to  the  lower  cervical  region  and  pass  out  into  the  sym- 
pathetic nervous  system  at  this  level.  The  centers  of  vaso- 
motor control  of  various  regions  of  the  body  are  indicated 
in  Fig.  111. 


THE    VISCERAL    AND    GUSTATORY    APPARATUS  2()8 

Ranson  and  von  Hess  ('15)  have  given  evidence  that,  in  the  spinal  cord 
of  cats  the  conduction  path  for  puin,  for  depression  of  blood  pressure  and 
for  respiratory  changes  lies  in  the  dorsal  part  of  the  lateral  funiculus  and 
that  there  is  a  second  pathway  involving  changes  in  blood  pressure  in  the 
fasciculus  dorso-lateralis  (Lissauer's  tract)  whose  stimulation  raises  the 
blood  pressure. 

Ranson  and  Billingsley  ('16)  have  later  shown  that  the  unmyelinated 
fibers  of  the  dorsal  spinal  roots  are  conductors  of  painful  impressions. 

Organs  of  Respiration.—  Oxygen  is  supplied  to  the  tissues 
of  the  body  in  a  great  variety  of  ways  in  different  animals. 
In  some  of  the  simpler  animals,  as  in  plants  generally,  oxygen 
is  simply  absorbed  from  the  surrounding  medium  by  the  ex- 
posed surfaces.  In  all  but  the  lowest  animals  there  is  a  blood- 
vascular  system  by  means  of  which  the  oxygen  absorbed  at  the 
surface  is  transferred  to  the  deeper  tissues.  In  insects,  how- 
ever, this  result  is  obtained  chiefly  by  a  different  apparatus, 
namely,  a  system  of  air  tubes  (tracheae)  which  ramify  among 
the  tissues  and  supply  oxygen  directly  to  the  functioning 
cells.  In  most  water-breathing  animals  a  portion  of  the 
surface  of  the  l)ody  is  lamellated  and  vascularized  to  form 
gills  to  faciliate  the  absorption  of  oxygen  by  the  blood-stream, 
and  in  air-breathing  vertebrates  lungs  are  developed  to  accom- 
plish the  same  result.  The  nervous  mechanisms  of  respira- 
tion will  differ  in  all  of  the  cases  cited  above,  and  it  is  only  in 
mammals  that  we  shall  here  consider  the  details  of  this 
mechanism. 

In  ordinary  oreathing,  mspiration  is  effected  by  actively  in- 
creasing the  volume  of  the  thoracic  cavity  and  thus  creating  a 
suction  tlirough  the  trachea,  while  expiration  is  the  result  of  the 
passive  return  of  the  organs  involved  to  their  former  positions 
by  reason  of  their  own  elasticity.  The  muscles  involved  in 
inspiration  belong  to  two  groups:  (1)  the  internal  apparatus, 
i.  e.,  the  diaphragm,  and  (2)  the  external  apparatus,  the  inter- 
costal and  other  muscles  of  the  body  wall.  These  are  all 
somatic  muscles.  In  forced  respiration  various  other  muscles 
act  in  an  accessory  way  during  both  inspiration  and  expiration. 

The  diaphragm  is  innervated  by  the  phrenic  nerve,  which 
takes  its  origin  from  the  fourth  and  fifth  cervical  spinal  nerves; 
and  the  intercostal  muscles  are  innervated  bv  ventral  spinal 
roots  arising  successively  from   all   thoracic  segments  of  the 


264 


INTRODUCTION    TO    NEUROLOGY 


spinal  cord  (Fig.  112).  The  accessory  muscles  are  in  part 
somatic  muscles  of  the  abdomen  and  shoulder  and  in  part 
special  visceral  muscles  of  the  head,  particularly  those  of  the 
glottis  (innervated  by  the  vagus)  and  of  the  nostrils  (inner- 
vated by  the  VII  cranial  nerve). 

The  anatomical  relations  just  described  imply  that,  although 
respiration  is  a  visceral  function,  in  mammals  the  necessary 


Dorsal  motor  X. 
nucleus 
Nucleus  of  fascic.  solitarius 

Fasciculus  solitariua 

Vagus  ganglion. 

Vagus  nerve. 

Tr.  solitario-spinalis, 

Sympathetic  ganglion 


Lung. 
Intercostal  nerve. 

Int«reostal  muscle. 
Phrenic  nerve 


iBlood-vessel 
Respiratory  center 


Fig.   112. 


Diaphragm 


-Diagriim   of   the  nervous  mechanism   of    respiration, 
from  Ram6n  y  Cajal.) 


(Modified 


movements  for  ordinary  breathing  are  performed  by  somatic 
muscles.  This  is  not  true  in  fishes.  Here  the  organs  of  respi- 
ration (gills)  are  strictly  visceral  structures  innervated  by  vis- 
ceral components  of  the  cranial  nerves,  whose  cerebral  center  is 
in  the  lower  part  of  the  medulla  oblongata  (the  area  visceralis 
of  Fig.  43,  p.  119). 

In  the  ordinary  breathing  of  mammals  the  act  of  inspiration 
is  effected  by  an  upward  and  outward  movement  of  the  ribs  and 
a  downward  movement  of  the  diaphragm.  Now,  if  the  spinal 
cord  be  cut  through  at  the  level  of  the  seventh  cervical  nerve 
the  respiratory  movement  of  the  ribs  is  entirely  abolished, 


THE   VISCERAL    AND    CJUSTATORY    APPARATUS  2(35 

though  the  movements  of  the  diaphragm  go  on  as  usual.  The 
continuity  of  the  thoracic  motor  nerves  which  innervate  the 
intercostal  muscles  with  their  centers  of  origin  in  the  spinal 
cord  is  undisturbed  by  this  operation,  yet  they  can  no  longer 
be  coordinated  in  the  respiratory  act.  If  in  another  animal 
the  spinal  cord  be  divided  at  the  level  of  the  third  cervical 
nerve,  i.  e.,  above  the  level  of  origin  of  the  phrenic  nerve,  the 
respiratory  movements  of  both  the  ribs  and  the  diaphragm 
cease,  even  though  the  spinal  cord  below  the  section  is  intact 
and  its  connection  with  the  peripheral  respiratory  apparatus 
is  undisturbed.  These  experiments  show  that  the  spinal 
segments  from  which  all  of  the  motor  respiratory  nerves  arise 
cannot  of  themselves  effect  the  coordinations  necessary  in 
respiration.  This  is  in  marked  contrast  with  many  other 
reactions  (both  visceral  and  somatic),  whose  performance  is 
still  possible  after  the  separation  of  the  spinal  cord  from  the 
brain. 

If  now,  in  a  third  animal,  the  medulla  oblongata  is  cut  across 
at  any  point  above  the  middle  of  its  length,  say  at  the  lower 
border  of  the  pons,  the  respiratory  processes  are  in  no  way 
disturbed.  This  shows  that  there  is  a  i-espiratory  correlation 
center  in  the  lower  half  of  the  medulla  oblongata,  that  is, 
somewhere  in  the  region  corresponding  to  the  "visceral  area" 
of  the  fish  brain. 

The  air  tubes  of  the  lungs  are  provided  with  smooth  muscle- 
fibers  by  which  their  caliber  may  be  contracted.  These  mus- 
cles are  innervated  by  the  vagus,  and  the  hyperexcitation  of 
their  motor  nerves  may  impede  respiration,  this  being  one  of 
the  factors  which  cause  asthma.  The  cerebral  center  from 
which  these  inti'insic  muscles  of  the  lungs  are  innervated  has 
been  shown  to  lie  in  the  middle  part  of  the  dorsal  motor  vagus 
nucleus  (Fig.  73,  niic.  dorsalis  vagi).  These  are  preganglionic 
neurons,  the  corresponding  postganglionic  neurons  lying  in 
sympathetic  ganglia  distiibuted  along  the  pulmonary  branches 
of  the  vagus  (Fig.  112). 

The  apparatus  described  in  the  preceding  paragraph  is,  how- 
ever, not  responsible  for  the  maintenance  of  the  regular  rhythm 
of  breathing.  Physiological  experiments  show  that  there  is 
somewhere  in  the   lower   part  of  the  medulla  oblongata  a 


266  INTRODUCTION  TO  NEUROLOGY 

respiratory  center  which  performs  this  function.  This  center 
may  be  excited  to  activity  directly  by  variations  in  the  compo- 
sition of  the  blood  which  reaches  it,  and  particularly  by 
variations  in  the  proportions  of  carbon  clioxid.  Its  activity 
may  also  be  modified  by  nervous  influences  reaching  it  through 
the  peripheral  afferent  nerves,  the  vagus  being  the  only  nerve 
which  appears  to  be  able  to  act  directly  on  the  respiratory 
center,  though  the  strong  excitation  of  almost  any  sensory 
nerve  of  the  body  may  under  some  circumstances  indirectly 
affect  the  respiratory  rhythm.  Coughing  and  sneezing  are 
special  cases  of  this  sort.  The  reflex  mechanism  of  the  cough 
is  illustrated  in  Fig.  113. 

Attempts  to  localize  the  respiratory  center  in  the  mammalian  medulla 
oblongata  more  accurately  have  led  to  contradictory  results.  The  old 
concejition  of  Flourens  that  there  is  a  minute  "vital  node"  under  the  low- 
est point  of  the  fourth  ventricle  which  is  the  respiratory  center  must  be 
abandoned.  Later  the  fasciculus  solitarius  was  identified  as  the  "respira- 
tory tract,"  and  the  nucleus  associated  with  this  tract  was  regarded  as 
the  respiratory  center,  but  further  experiment  has  shown  that  this  is 
not  an  exact  statement  of  the  case.  Some  physiological  experiments 
have  suggested  that  the  respiratory  rhythm  is  maintained  by  a  center 
in  the  reticular  formation  of  the  vagus  region  ventrally  of  the  fasciculus 
solitarius. 

It  has  recently  been  shown,  as  stated  above,  that  afferent  visceral  fibers 
from  the  lungs  whose  cell  bodies  lie  in  the  vagus  ganglion  enter  the  fascicu- 
lus solitarius,  and  it  is  known  that  from  the  nucleus  of  this  tract  a  "trac- 
tus  solitario-spinahs"  (Fig.  112)  descends  into  the  motor  centers  of  the 
upper  segments  of  the  spinal  cord.  This  descending  visceral  spinal 
tract  probably  plays  some  part  in  the  regulation  of  respiration,  though 
not  the  chief  role.  Ramon  y  Cajal  and  Kappers  believe  that,  while  the 
upper  part  of  the  nucleus  of  the  fasciculus  solitarius  has  nothing  to  do 
with  respiration,  the  lower  end  of  this  nucleus  (commissural  nucleus  of 
Cajal,  see  Figs.  71,  112,  and  114)  is  a  true  respiratory  center.  Ramon  y 
Cajal,  in  fact,  thinks  that  this  nucleus  serves  both  for  reflexes  excited  by 
the  sensory  pulmonary  nerves  and  also  for  the  normal  respiratory 
rhythm  excited  by  carbon  dioxid  in  the  blood.  This  hypothesis  is 
not  supported  by  direct  physiological  experiment,  and  for  the  present 
we  must  content  ourselves  with  the  statement  that  the  true  respiratory 
center  has  not  been  accurately  located  anatomically.  Figure  112  may 
be  regarded  as  a  true  picture  of  the  essential  relations  of  the  respiratory 
nerves,  with  the  reservation  that  the  position  of  the  respiratory  center  is 
not  precisely  known. 

There  is  also  a  reflex  center  for  the  regulation  of  respiration  in  the  me- 
dial wall  of  the  thalamus  and  others  have  been  described  in  different  parts 
of  the  brain  stem.  The  entire  respiratory  mechanism  is  also  under 
partial  voluntary  control  from  the  cerebral  cortex. 

AVhile  manv  features  of  the  central  respiratory  mechanism 


THE    VISCERAL    AND    OITSTATORV    API'AltATUS 


267 


Stomach- 


Dorsal  motor 
vagus  nu- 
cleus 


onie  neuron 


Fig.  113 — Diagram  of  the  nervous  mechanisms  of  coughing  and  vomiting. 
In  the  cough  an  irritation  of  the  mucous  membrane  of  the  larynx  is  trans- 
mitted to  the  nucleus  of  the  fasciculus  solitarius,  from  which  the  tractus 
solitario-spinalis  passes  downward  to  the  motor  centers  of  the  spinal  cord 
for  the  innervation  of  the  muscles  of  the  diaphragm,  the  abdominal  wall, 
and  the  ribs  which  cooperate  in  the  production  of  the  cough.  In  vomiting, 
an  irritation  of  the  stomach  is  carried  by  sensory  fibers  of  the  vagus  to  the 
nucleus  of  the  fasciculus  solitarius,  from  which  the  pathway  is  as  before  to 
the  spinal  motor  centers  for  the  innervation  of  the  diaphragm  and  abdominal 
wall.  In  this  case  there  is  also  an  excitation  of  the  dorsal  motor  vagus 
nucleus,  from  which  preganglionic  fibers  go  out  into  the  vagus  nerve  for  a 
sympathetic  ganglion  in  the  gastric  plexuses,  from  which,  in  turn,  post- 
ganglionic fibers  pass  to  the  muscles  of  the  stomach  which  participate  in  the 
ejection  of  its  contents.  The  diagram  is  suggested  by  one  in  Ramou  y  Cajal's 
text-book,  though  greatly  modified. 


268  INTRODUCTION    TO    NEUROLOGY 

remain  obscure,  it  seems  evident  that  the  location  of  the  chief 
respiratory  center  in  the  "visceral  area"  of  the  lower  part  of 
the  medulla  oblongata  instead  of  the  portions  of  the  spinal  cord 
directly  connected  with  the  respiratory  muscles  is  a  survival  of 
the  ancestral  condition  found  in  fishes,  where  the  entire  respira- 
tory function  is  carried  on  by  a  visceral  apparatus  (gills)  inner- 
vated from  the  vagus  region. 

Organs  of  Digestion. — Hunger  seems  to  be  a  complex  in 
which  at  least  three  factors  are  present:  (1)  Specific  hunger 
pangs  due  to  waves  of  muscular  contraction  in  the  stomach 
(Cannon,  Carlson);  (2)  appetite,  or  craving  for  food  regardless 
of  the  state  of  the  stomach;  (3)  general  malaise  from  starvation 
of  the  tissues  and  weakness.  Appetite  may  persist  after 
section  of  the  vagus  nerves  and  is  probably  a  sensation  distinct 
from  the  hunger  pangs. 

The  ordinary  processes  of  digestion  are  carried  on  partly  by 
automatic  activities  of  the  organs  without  nervous  control 
(see  p.  249),  and  partly  by  the  intrinsic  sympathetic  nervous 
system  of  the  digestive  organs.  Throughout  the  length  of  the 
digestive  tract  there  are  two  sympathetic  ganglionated  plexuses. 
One  of  these  is  located  between  the  muscular  coats  of  the  stom- 
ach and  intestine,  known  as  the  myenteric  or  Auerbach's  plexus ; 
the  other  lies  immediately  under  the  lining  mucous  membrane 
and  is  known  as  the  submucous  or  Meissner's  plexus.  It  has 
been  shown  physiologically  that  the  local  reflexes  concerned  in 
the  typical  peristaltic  contractions  of  the  digestive  tube  are 
effected  chiefly  by  the  myenteric  plexus.  Accordingly,  this 
reflex  is  called  by  Cannon  the  myenteric  reflex. 

The  entire  digestive  mechanism  (like  most  of  the  other 
visceral  systems)  may  also  be  influenced  indirectly  by  nervous 
impulses  arising  in  the  cerebral  cortex,  though  these  organs 
are  not  under  direct  voluntary  control.  It  is  well  known  that 
the  digestive  processes  are  especially  sensitive  to  emotional 
states,  pleasurable  experiences  promoting  digestion  and  painful 
or  disagreeable  emotions  inhibiting  it.  These  facts  can  be 
studied  on  laboratory  animals  under  experimental  conditions 
(Cannon).  A  large  amount  of  information  regarding  the 
physiology  of  digestion  has  recently  been  gathered  by  Carlson 
from  the  study  of  a  man  with  an  artificial  opening  into  the 


THE   VISCERAL    AND    GUSTATORY    APPARATUS  269 

stomach  (gastric  fistula),  permitting  direct  observation  of  the 
stomach  at  all  times. 

The  salivary  glands  are  excited  to  secretion  from  two  nuclei 
of  the  medulla  oblongata,  the  superior  salivatory  nucleus  (Figs. 
71,  114),  whose  preganglionic  fibers  go  out  with  the  VII  cranial 
nerve  for  the  sublingual  and  submaxillary  salivary  glands,  and 
the  inferior  salivatory  nucleus  (Figs.  71,  73,  114),  whose  fibers 
go  out  with  the  IX  nerve  for  the  parotid  gland.  The  secretion 
of  saliva  may  be  produced  either  as  a  simple  reflex  from  the 
presence  of  food  in  the  mouth  through  the  gustatory  nerves  and 
fasciculus  solitarius,  or  as  so-called  psychic  secretion  excited  by 
the  sight  or  thought  of  food.  All  of  the  digestive  secretions 
are  susceptible  to  this  sort  of  indirect  excitation,  as,  indeed,  are 
most  other  processes  which  are  under  the  control  of  the  cerebro- 
spinal visceral  nervous  system.  These  visceral  reactions,  in 
their  turn,  are  reported  back  to  the  central  nervous  system  and 
no  doubt  play  a  very  large  part  in  shaping  the  organic  back- 
ground of  the  entire  conscious  life  (see  p.  288). 

Students  of  animal  behavior  are  in  the  habit  of  investigating 
the  ability  of  animals  to  make  simple  associations  by  training 
them  to  perform  particular  acts  under  conditions  such  that  the 
normal  stimulus  to  the  act  is  always  accompanied  by  a  second 
stimulus  of  a  different  type.  After  many  repetitions  the  re- 
sponse may  be  obtained  by  presenting  the  second  or  collateral 
stimulus  without  the  first.  For  the  nervous  mechanism  of 
"associative  memory"  of  this  sort  see  p.  67.  Pawlow  has 
found  that  variations  in  the  amount  of  saliva  secreted  form  an 
especially  good  index  of  associations  of  this  type,  and  he  has 
used  this  method  extensively  in  analyzing  complex  reactions, 
or  conditional  reflexes,  as  he  calls  them.  See  the  summary 
of  his  researches  in  the  paper  by  Morgulis  cited  in  the  appended 
bibliography. 

Tactile  sensibility  is  entirely  absent  throughout  the  entire 
alimentary  canal  from  the  esophagus  to  the  rectum,  and  the 
same  holds  true  for  most  of  the  other  deep-seated  viscera  of  the 
body.  Even  the  substance  of  the  brain  is  insensitive  to  any 
kind  of  mechanical  irritation.  Sensibility  to  changes  in  tem- 
perature is  feebly  developed  or  absent  in  most  of  the  viscera, 
the  esophagus  and  anal  canal  being  very  sensitive  to  heat  and 


270  INTRODUCTION    TO    NEUROLOGY 

cold,  while  the  stomach  and  colon  are  feebly  sensitive  to  these 
stimuli.  The  entire  alimentary  canal  is  insensitive  to  hydro- 
chloric and  organic  acids  in  concentrations  far  in  excess  of 
what  ordinarily  occurs  in  either  normal  or  pathological  con- 
ditions. The  contact  of  alcohol  with  all  parts  of  the  mucous 
membrane  of  the  alimentary  canal  gives  rise  to  a  sensation 
of  warmth.  This  sensation  is  different  in  character  from  that 
caused  by  hot  fluids  and  is  probably  excited  through  the 
sympathetic  nerves,  while  the  sensation  of  warmth  felt  in 
consequence  of  the  passage  of  hot  fluid-  through  the  esophagus 
is  excited  through  the  vagus. 

The  demonstrated  absence  of  tactile  sensibility  throughout 
the  mucous  membrane  of  the  stomach  and  intestine  is  consid- 
ered by  Hertz  to  indicate  that  the  sensations  of  fulness  arising 
from  the  distention  of  different  parts  of  the  alimentary  canal 
are  due  to  the  stretching  of  the  muscular  coat,  and  that, 
therefore,  these  are  to  be  regarded  as  varieties  of  the  muscle 
sense.  The  same  may  also  be  true  of  the  bladder.  The  free 
nerve-endings  (see  Fig.  33,  p.  95)  known  to  be  present  in  these 
mucous  membranes,  particularly  in  the  bladder,  may,  how- 
ever, share  in  exciting  these  sensations,  for  these  membranes 
may  well  be  sensitive  to  stretching,  even  though  quite  insen- 
sitive to  simple  pressure.  The  only  immediate  cause  of  true 
visceral  pain  is  tension,  and  it  is  stated  by  Hertz  that,  so  far 
as  the  alimentary  canal  is  concerned,  this  tension  is  exerted 
on  the  muscular  coat,  not  on  the  mucous  lining.  See  the 
further  discussion  of  visceral  pain,  p.  278. 

The  vomiting  reflex  may  be  caused  by  excitations  of  sensory 
termini  of  the  vagus  nerve  in  the  stomach,  which  are  trans- 
mitted to  the  nucleus  of  the  fasciculus  solitarius  in  the  medulla 
oblongata,  whence  the  nervous  impulses  are  distributed  as 
shown  in  Fig.  113  to  the  appropriate  motor  centers. 

The  Gustatory  Apparatus. — Taste,  like  smell,  is  a  chemical 
sense  (see  pp.  80,  96,  242).  Physiologically,  it  is  classed  by 
Sherrington  as  an  interoceptive  or  visceral  sense,  and  its 
primary  cerebral  center  is  intimately  joined  to  the  general 
visceral  sensory  center  in  the  nucleus  of  the  fasciculus  soli- 
tarius. Unlike  the  general  visceral  sensory  system,  however, 
its  peripheral  fibers  have  no  connection  with  the  sympathetic 


THE    VISPERAL    AND    GUSTATORY    APPARATUS 


271 


VIII 

IX  motor 

X  motor 

XI  pars  bulbaris 

XI  pars  sp'malis 

Nuc.  dorsalis  X 

Nuc.  ambiguus 


Ala  cinerea 
Fasciculus  solitarius 
Nuc.  commissiiralis  Cajal 

Nuc.  spinalis  V 


Fig.  114. — Diagram  of  the  visceral  afferent  and  efferent  connections  in 
the  medulla  oblongata,  based  on  Fig.  71;  compare  also  Figs.  77  and  S6.  The 
afferent  rootd  and  centers  arc  indicated  on  the  right  side;  the  eft'erent,  on 
the  left.  Visceral  sensory  fibers  enter  by  the  VII  nerve  (pars  intermedia 
of  Wrisberg,  VII  pars,  int.)  and  by  the  IX  and  X  nerves.  These  root-fibers 
include  both  general  visceral  sensory  and  gustatory  fibers,  all  of  -which  enter 
the  fasciculus  solitarius.  (Fibers  of  the  IX  and  X  nerves  also  enter  the 
spinal  V  tract;  but  since  these  are  somatic  sensory  fibers  from  the  auricular 
branch  they  are  not  included  in  the  diagram.  For  further  details  on  the 
composition  of  these  cranial  nerves  see  the  table  on  pp.  160,  161.) 

On  the  left  side  of  the  figure  the  general  visceral  efferent  nuclei  are  indi- 
cated by  small  dots  and  the  special  visceral  nuclei  by  large  dots.  The  latter 
comprise  the  motor  V  nucleus  for  the  jaw  muscles,  the  motor  VII  nucleus  for 
the  muscles  related  to  the  hyoid  bone  and  the  general  facial  musculature, 
and  the  nucleus  ambiguus  supplying  striated  muscles  of  the  pharynx  and 
larynx  by  way  of  the  IX  and  X  nerves.  Three  general  visceral  efferent 
nuclei  are  indicated — the  dorsal  motor  nucleus  of  the  vagus  under  the  ala 
cinerea  and  the  superior  and  inferior  salivatory  nuclei.  The  superior  nucleus 
{nuc.  sal.  sup.)  supplies  the  sublingual  and  submaxillary  salivary  glands  bj- 
way  of  the  VII  nerve  (pars  intermedia  of  A^'risberg),  and  the  inferior  nucleus 
{nuc.  sal.  inf.)  supplies  the  parotid  salivary  gland  by  way  of  the  IX  nerve. 
All  of  the  general  visceral  efferent  fibers  are  preganglionic  sympathetic  fibers 
(see  p.  256)  which  end  in  symijathetic  ganglia,  whence  postganglionic  fibers 
carry  the  nervous  impulses  onward  to  their  respective  destinations. 


272 


INTRODUCTION    TO    NEUROLOGY 


nervous  system  and  the  reactions  may  be  vividly  conscious. 
The  end-organs,  or  taste-buds  (Fig.  35,  p.  96),  are  present  in 
the  mucous  membrane  of  the  tongue,  soft  palate,  and  pharynx 
and  are  innervated  by  the  VII  and  IX  cranial  nerves;  there 
are  a  few  taste-buds  also  on  the  larynx  and  epiglottis  which  are 
probably  supplied  by  the  vagus  (J.  G.  Wilson).  All  of  these 
peripheral  gustatory  fibers,  upon  entering  the  medulla  o})lon= 


Fig.  115. — Diagram  showing  some  of  the  various  courses  which  have  been 
advocated  for  the  taste  fibers  in  man.  The  courses  advocated  in  this  work 
are  shown  by  heavy  black  lines;  other  suggested  courses  are  indicated  by 
broken  or  dotted  lines:  fac.  rt.,  motor  facial  root;  G.G.,  Gasserian  ganglion; 
G.g.,  geniculate  ganglion;  G.  otic,  otic  ganglion;  G.  petr.,  ganglion  petrosum; 
G.  sp.,  sphenopalatine  ganglion;  g.  s.  p.,  great  superficial  petrosal  nerve; 
N.  fac,  facial  trunk;  A''.  Jac,  Jacobson's  or  the  tympanic  nerve;  A'',  vid., 
vidian  nerve;  Rami  anast.,  anastomotic  rami  between  the  geniculate  ganglion 
and  tympanic  plexus  and  the  small  and  great  superficial  petrosal  nerves 
respectively;  s.  s.  p.,  small  superficial  petrosal  nerve;  Tymp.,  tympanum. 
(After  Gushing.) 

gata,  terminate  in  the  nucleus  of  the  fasciculus  solitarius 
(Figs.  71,  72,  73,  114)  along  with  those  of  general  visceral 
sensibility,  those  of  the  gustatory  system  probably  ending 
farther  forward  (toward  the  mouth)  in  this  nucleus  than  those 
of  the  general  visceral  systems. 

There  has  been  considerable  controversy  as  to  the  exact 
course  taken  by  the  peripheral  nerves  of  taste  on  their  way  to 
the  brain,  many  clinical  neurologists  believing  that  all  of  these 


THE   VISCERAL    AND    GUSTATORY    APPARATUS 


273 


fibers  enter  the  medulla  oblongata  through  the  root  of  the  V 
cranial  nerve.  It  has  now  been  clearly  shown  by  the  studies 
of  Gushing  and  others  that  the  \'  nerve  takes  no  part  in  the 
innervation  of  taste-buds.  Figure  115  shows  in  continuous 
lines  the  true  coiu'ses  of  the  nerve-fibers  from  the  taste-buds 
of  the  tongue  through  the  VII  and  IX  nerves,  and  in  broken 
and  dotted  lines  some  of  the  other  courses  which  have  })een 
suggested. 

In  fishes  the  gustatory  system  is  much  more  extensively  developed  than 
in  mammals,  especially  the  vagal  part  which  supplies  taste-buds  in  the  gill 
region.     In   some  sper-ics  of  fishes,  moreover,  taste-buds  appear  in  great 


Fig.  116. — The  cutaneous  gustatorj'  branches  arising  from  the  geniculate 
ganglion  of  the  facial  nerve  of  the  catfish  (Ameiums  melas),  projected  upon 
the  right  side  of  the  body.  Spinal  cord  and  brain  stippled.  The  geniculate 
ganglion,  its  roots  and  cutaneous  branches  are  drawn  in  black;  the  branches 
of  this  nerve  distributed  to  the  mucous  lining  of  the  mouth  cavity  are  omitted, 
Taste-buds  are  found  in  all  parts  of  the  outer  skin  to  which  these  branches 
are  distributed. 


numbers  in  the  outer  skin,  and  these  are  in  all  cases  innervated  from  the 
VII  cranial  nerve.  In  the  common  horned-pouts  or  catfishes  and  in  the 
carps  and  suckers  these  cutaneous  taste-buds  are  distributed  over  prac- 
•tically  the  entire  body  surface,  and  especially  on  the  barblets.  The  dis- 
tribution of  these  cutaneous  gustatorj'  branches  of  the  facial  nerve  in  the 
common  buUpout,  Ameiurus,  is  shown  in  Fig.  116.  These  sense-organs 
and  their  nerves  are  entirely  independent  of  those  of  the  lateral  line 
sensor)^  sj'stem  and  of  the  ordinarj'  tactile  s.ystem,  though  the  gustatory 
and  the  tactile  systems  have  been  shown  experimentally  to  cooperate 
in  the  selection  of  food.  The  primary  terminal  nuclei  of  these  gustatory 
nerves  make  up  by  far  the  larger  part  of  the  visceral  area  (Fig.  43,  p.  119) 
of  fish  brains,  and  in  some  species  these  centers  are  enormously  enlarged, 
as  in  the  carp  (Fig.  139  (2),  p.  337). 
18 


274  INTRODUCTION    TO    NEUROLOGY 

The  primary  sensory  center  for  the  nerves  of  taste  in  the 
nucleus  of  the  fasciciikis  sohtarius  is  very  intimately  connected 
with  all  of  the  motor  centers  of  the  medulla  oblongata  for  the 
reactions  of  mastication  and  swallowing,  and  also  with  the 
motor  centers  of  the  spinal  cord.  The  ascending  path  from 
the  primary  gustatory  nucleus  to  the  thalamus  and  cerebral 
cortex  is  wholly  unknown  in  the  human  body.  A  gustatory 
center  is  believed  to  exist  in  the  cortex  of  the  gyrus  hippocampi 
near  the  anterior  end  of  the  temporal  lobe.  In  fishes,  where 
this  ascending  gustatory  path  is  much  larger,  it  has  been  fol- 
lowed to  the  roof  of  the  midbrain  and,  after  a  synapse  here, 
to  the  region  of  the  hypothalamus  (Herrick,  1903,  1905,  1908). 

Visceral  Efferent  Centers. — The  arrangement  of  the  visceral 
efferent  nuclei  and  nerve-roots  of  the  medulla  oblongata  is 
shown  in  Fig.  114.  There  is  also  a  general  visceral  efferent 
component  of  the  III  cranial  nerve  (Fig.  71,  p.  168,  nuc. 
III.  E-W.),  whose  fibers  pass  out  through  this  nerve  to  the 
ciliary  ganglion  in  the  orbit,  which  in  turn  connects  with  the 
intrinsic  muscles  of  the  eyeball  in  the  ciliary  process  and  iris. 
These  fibers  are  involved  in  the  movements  of  accommodation 
of  .the  eye  for  varying  distances  and  in  the  regulation  of  the 
diameter  of  the  pupil.  The  nucleus  of  the  fasciculus  solitarius 
is  connected  through  the  reticular  formation  with  all  of  the 
motor  centers  of  the  medulla  oblongata  for  the  reactions  of 
mastication  and  swallowing  and  for  many  other  movements; 
from  this  nucleus  there  is  a  descending  tract  to  the  motor 
centers  of  the  spinal  cord,  the  tractus  solitario-spinalis  (Figs. 
112  and  113).  There  is  also  a  connection  with  the  superior 
and  inferior  salivatory  nuclei  of  the  VII  and  IX  nerves.  The 
excitation  of  the  gustatory  fibers  of  these  nerves  by  the 
presence  of  food  in  the  mouth  is  carried  to  the  nucleus  of  the 
fasciculus  sohtarius  and  thence  through  the  reticular  formation 
to  the  salivatory  nuclei,  from  which  the  flow  of  saliva  is  excited. 
There  are  other  connections  with  the  motor  centers  of  the 
spinal  cord  through  the  descending  fibers  of  the  fasciculus 
solitarius,  some  of  these  fibers  crossing  to  the  opposite  side  in 
the  vicinity  of  the  commissural  nucleus  of  Cajal  (Fig.  114). 

Summary. — The  cerebro-spinal  visceral  systems  fall  into  a 
general  group  related  peripherally  to  the  sympathetic  nerves 


JIIE   VISCKRAL    AND    GUSTATORY    APPARATUS  275 

and  a  special  group  independent  of  the  sympathetic.  The 
second  group  includes  the  apparatus  for  taste  and  probably 
for  smell.  The  central  innervation  of  the  viscera  is  partly 
from  the  spinal  and  midbrain  regions,  but.  chiefly  from  the 
visceral  area  of  the  medulla  oblongata.  The  heart  and  blood- 
vessels have  a  double  innervation  derived  from  both  the  spinal 
and  the  bulbar  visceral  centers,  and  the  nervous  control  of 
the  organs  of  circulation  is  very  complex.  Respiration  in 
lower  vertebrates  is  effected  by  strictly  visceral  structures  and 
is  controlled  from  the  visceral  area  of  the  medulla  oblongata. 
In  mammals  the  muscles  of  ordinary  respiration  are  all  of  the 
somatic  type,  but  the  centers  of  control  are  retained  in  the 
visceral  area  of  the  oblongata.  The  sensations  related  to  the 
digestive  tract  are  served  chiefly  (though  not  exclusively) 
by  the  vagus.  There  are  special  salivatory  nuclei  related 
to  the  VII  and  IX  cranial  nerves.  The  nerves  of  taste  are  the 
VII,  IX,  and  to  a  very  limited  extent  (in  man)  the  X  pairs 
of  cranial  nerves.  The  primary  cerebral  gustatory  center  is 
in  the  upper  part  of  the  nucleus  of  the  fasciculus  solitarius, 
but  the  cortical  path  is  unknown. 

Literature 

Any  of  the  larger  text-books  of  physiology  will  give  further  details  of 
the  visceral  reactions.  For  a  very  brief  and  simple  account  of  the  cir- 
culatory apparatus  see  the  book  by  Stiles  (pp.  118-125)  cited  below.  The 
experiments  of  Molhant  have  given  us  the  most  detailed  information  re- 
garding the  visceral  functions  of  the  vagus  and  their  centers  in  the  medulla 
oblongata. 

Cannon,  W.  B.  1898.  The  Movements  of  the  Stomach  Studied  by 
Means  of  the  Rontgen  Rays,  Amer.  Jour.  Physiol.,  vol.  i,  pp.  359-382. 

— .  1902.  The  Movements  of  the  Intestines  Studied  by  Means  of  the 
Rontgen  Rays,  Amer.  Jour.  Phj^siol.,  vol.  vi,  p.  251 

— .  1912.  Peristalsis,  Segmentation,  and  the  Myenteric  Reflex,  Amer. 
Jour.  Physiol.,  vol.  xxx,  pp.  114-128 

Cannon,  W.  B.,  and  Washburn,  A.  L.  1912.  An  Explanation  of 
Hunger,  Amer.  Jour.  Physiol.,  vol.  xxix,  pp.  441-450. 

Carl.son,  a.  J.,  and  Others.  1912-1918.  Contributions  to  the  Physi- 
ologj'  of  the  Stomach,  Amer.  Jour.  Phj^sioL,  vols,  xxxi-xlv. 

Carlson,  A.  J.  1916.  The  Control  of  Hunger  in  Health  and  Disease, 
University  of  Chicago  Press. 

Cu.'=!HiNO,  H.  1903.  The  Taste  Fibers  and  Their  Independence  of  the 
N.  Trigeminus,  Jolms  Hopkins  Hcspital  Bulletin,  vol.  xiv,  pp.  71-78. 

Herrick  C.  Judson.  1903.  The  Organ  and  Sense  of  Taste  in  Fishes, 
Bui.  U.  S.  Fish  Commission  for  1902,  pp.  237-272. 


276  INTRODUCTION  TO  NEUROLOGY 

Heerick,  C.  Judson.  1905.  The  Central  Gustatory  Paths  ui  the 
Brains  of  Bony  Fishes,  Jour.  Comp.  Neurol.,  vol.  xv,  pp.  375-456. 

— .  1908.  On  the  Commissura  Infima  and  Its  Nuclei  in  the  Brains  of 
Fishes,  Jour.  Comp.  Neurol.,  vol.  xviii,  pp.  409-431. 

Hertz,  A.  F.  1911.  The  Sensibility  of  the  Alimentary  Canal,  Lon- 
don, Oxford  University  Press. 

Kappers,  C.  U.  a.  1914.  Der  Geschmack,  perifer  und  central,  zug- 
leich  eine  Skizze  der  phylogenetischen  Veranderungen  in  der  sensibelen 
VII,  IX,  und  X  Wurzeln,  Psychiat.  en  Neurol.,  Bladen,  pp.  1-57. 

MoLHANT,  M.  1910-1913.  Le  nerf  vague:  Etude  anatomique  et  ex- 
perimentale,  Le  Nevraxe,  vols,  xiii-xv. 

MoRGULis,  S.  1914.  Pawlow's  Theory  of  the  Function  of  the  Central 
Nervous  System  and  a  Digest  of  Some  of  the  More  Recent  Contributions 
to  this  Subject  from  Pawlow's  Laboratory,  Jour.  Animal  Behavior,  vol.  iv, 
pp.  362-379. 

Pawlow,  I.  1913.  The  Investigation  of  the  Higher  Nervous  Func- 
tions, Brit.  Med.  Jour.,  vol.  ii  for  1913,  pp.  973-978. 

Ranson,  S.  W.,  and  von  Hess,  C.  L.  1915.  The  Conduction  within 
the  Spinal  Cord  of  the  Afferent  Impulses  Producing  Pain  and  the  Vaso- 
motor Reflexes,  Am.  Jour.  Physiol.,  vol.  xxxviii,  pp.  128-152. 

Ranson,  S.  W.,  and  Billingsley,  P.  R.  1916.  The  Conduction  of 
Painful  Afferent  Impulses  in  the  Spinal  Nerves,  Am.  Jour.  Physiol.,  vol. 
xl,  pp.  571-584. 

Sheldon,  R.  E.  1909.  The  Phylogeny  of  the  Facial  Nerve  and 
Chorda  Tympani,  Anat.  Record,  vol.  iii,  pp.  593-617. 

— .  1909.  The  Reactions  of  the  Dogfish  to  Chemical  Stimuli,  Jour. 
Comp.  Neurol.,  vol.  xix,  pp.  273-311. 

Stiles,  P.  G.  1915.  The  Nervous  System  and  Its  Conservation, 
Philadelphia. 

Wilson,  J.  G.  1905.  The  Structure  and  Function  of  the  Taste-buds 
of  the  Larynx,  Brain,  vol.  xxviii,  pp.  339-351. 


CHAPTER  XVIII 
PAIN  AND  PLEASURE 

Few  problems  in  neurology  are  more  difficult  and  involved 
than  those  centering  about  the  nerves  of  painful  sensibility. 
This  question  is  intimately  related  with  the  disagreeable  and 
pleasurable  feelings  and  with  the  affective  and  emotional  life 
as  a  whole.  Nearly  all  sensations,  whether  of  the  somatic  or 
visceral  series,  appear  to  have  an  agreeable  or  disagreeable 
quahty  (quale).  There  is  difference  of  opinion  as  to  whether 
any  sensation  is  wholly  indifferent  in  this  respect.  There  are, 
however,  two  factors  in  this  situation  which  have  not  always 
been  distinguished  and  whose  introspective  analysis  is  very 
difficult.  In  the  first  place,  many  sensations  are  as  such  pain- 
ful or  pleasurable,  and  in  the  second  place  the  related  apper- 
ceptions, ideas,  etc.,  may  have  an  agreeable  or  disagreeable 
feeling  tone.  The  intimate  relation  of  these  two  factors  in 
consciousness  probably  grows  out  of  a  similarity  in  the  type 
of  physiological  process  involved  in  their  neurological  mechan- 
isms, and  this,  in  turn,  may  rest  on  the  fact  that  the  two  mech- 
anisms in  question  have  had  a  common  evolutionary  origin. 

The  stimulation  of  some  of  the  sense  organs  results  in  the  so- 
called  sensation  of  pain  with  no  other  quality  recognizable;  this 
is  true  of  the  cornea,  of  the  tooth  pulps,  of  the  tympanic 
membrane,  and  of  the  "pain  spots"  of  the  outer  skin.  This 
fact  would  suggest  that  there  is  a  special  system  of  neurons  (or 
at  least  of  receptors,  see  p.  90)  for  pain  as  for  the  other  senses. 
But,  on  the  other  hand,  the  supernormal  stimulation  of  most 
other  sense  organs  may  result  in  a  very  similar  type  of  pain, 
though  in  this  case  the  painful  quality  is  accompanied  bj^  the 
normal  sensor}^  quality  of  the  organ  in  question  unless  the 
stimulation  is  excessively  strong.  From  this  it  would  appear 
that  most  sensory  nerves  may  upon  occasion  function  as  pain 
nerves.     In  other  cases  normal  stimulation  of  a  sense  organ 

277 


278  INTRODUCTION.  TO    NEUROLOGY 

may  result  in  a  sensation  of  the  quality  typical  for  the  organ  in 
question,  to  which  there  is  added  an  agreeable  or  disagreeable 
quality  which  may  be  very  pronounced,  the  disagreeable 
quality  not  being  painful  in  the  ordinary  sense  of  that  term. 
This  mixed  quality  of  normal  sensations  is  illustrated  by 
certain  odors  and  savors,  and  on  the  agreeable  side  by  certain 
sensations  of  tickle  and  warmth.  Finally,  some  ideational 
processes  have  an  agreeable  or  disagreeable  quality,  and  these, 
in  turn,  are  very  intimately  related  with  the  emotions  and  with 
esthetic  and  appreciative  functions  of  the  most  complex 
psychic  sort,  as  well  as  with  questions  of  habitual  emotional 
attitude  and  temperament. 

The  superficial  parts  of  the  body  which  are  more  directly  ex- 
posed to  traumatic  injury  are,  in  general,  more  sensitive  to  pain 
than  are  the  deeper  parts,  and  painful  stimuli  here  can  be  more 
accurately  localized.  In  some  parts,  like  the  conjunctiva  of 
the  eyeball,  where  very  slight  irritation  may  seriously  interfere 
with  the  function,  very  gentle  stimulation  gives  rise  to  acute 
pain,  and  no  other  sensory  quahty  may  be  present. 

Surgeons  find  that  the  brain  membranes  are  sensitive  to 
mechanical  injury,  especially  to  stretching  or  pulling.  The 
brain  substance  itself,  however,  is  quite  insensitive  to  pain 
from  either  mechanical  or  chemical  stimulation.  The  deeper 
viscera  of  the  thorax  and  abdomen  are  insensitive  to  pinching, 
cutting  with  a  sharp  instrument,  or  other  mechanical,  chemical, 
or  thermal  stimuli,  though  they  are  sensitive  to  pains  arising 
from  internal  disorders,  as  in  colic  (p.  270).  The  visceral 
portions  of  the  pleural  and  peritoneal  membranes  are  insen- 
sitive to  pain,  but  their  parietal  portions,  forming  the  inner- 
most layer  of  the  body  wall,  are  sensitive,  and  these  pains  can 
be  accurately  localized  (Capps). 

From  these  considerations  it  appears  that  pain  is  an  adaptive 
function  which  is  present  only  where  it  is  of  value  to  give  warn- 
ing of  noxious  influences  liable  to  injure  the  body  unless  re- 
moved. (See  the  excellent  discussion  by  Sherrington  in 
Schafer's  Physiology,  vol.  ii,  pp.  965-1001.) 

Pains  of  this  sort  are  physiologically  similar  to  other  extero- 
ceptive sensations,  that  is,  they  have  a  definite  localization  and 
are  externally  projected  like  other  somatic  sensations.     But 


PAIN    AND    PLEASURE  279 

other  pains  and  discomforts  (especially  those  related  to  the 
visceral  functions)  and  all  pleasurable  feelings  are  devoid  of  this 
external  projicience  and  are  experienced  merely  as  a  non-local- 
ized awareness  of  malaise  or  well-being  (see  p.  288).  They  are 
also  more  variable  in  relation  to  habit,  mental  attitude,  fatigue, 
and  general  health.  This  latter  group  of  affective  processes  is 
so  different  from  the  ordinary  sensations  as  to  make  it  desirable 
to  consider  them  separately,  and,  as  will  appear  beyond,  they 
probably  involve  a  quite  different  series  of  nervous  processes. 
There  has  been  much  controversy  regarding  the  pathway 
taken  by  painful  impulses  through  the  spinal  cord  and  brain 
stem,  and  it  is  probable  that  this  pathway  is  very  complex. 
All  painful  impulses  carried  by  the  spinal  nerves,  no  matter 
what  the  peripheral  source,  are  discharged  immediately  upon 
entering  the  spinal  cord  into  its  gray  matter,  and  after  a 
synapse  here  the  nerve-fibers  of  the  second  order  seem  to  take 
several  courses.  The  recent  experiments  of  Karplus  and 
Kreidl  (1914)  go  to  show  that  the  ascending  impulses  of  pain- 
ful sensibility  in  the  spinal  cord  of  cats  follow  a  chain  of  short 
neurons,  some  of  whose  axons  immediately  cross  to  the  oppo- 
site side  of  the  cord  and  some  ascend  on  the  same  side.  These 
short  fibers  belong  to  the  fasciculus  proprius  system  (p.  138), 
and  the  nervous  impulse  is  at  frequent  intervals  returned  to 
the  gray  matter  to  pass  from  one  neuron  to  another,  and  it 
may  cross  the  midplane  repeatedly.  This  diffuse  method  of 
conduction  appears  to  be  the  primitive  arrangement.  In  the 
human  spinal  cord  it  is  probably  present  to  a  limited  extent, 
but  has  been  lai'gely  supplanted  by  a  more  direct  pathway 
in  the  spinal  lemniscus,  whose  precise  localization  has  been 
determined  by  the  clinical  studies  of  Henry  Head  and  others 
(pp.  150,  189).  This  direct  path  for  fibers  of  painful  sensi- 
bility includes  axons  of  neurons  of  the  dorsal  gray  column, 
which  immediately  cross  to  the  opposite  side  of  the  cord 
and  ascend  directly  to  the  thalamus.  Injury  to  this  path  in  the 
human  body  may  cause  complete  insensitivity  to  both  supei-- 
ficial  and  deep  pain  on  the  opposite  side  of  the  body  below  the 
site  of  the  injury,  without  loss  of  general  tactile  sensibility. 
The  two  methods  of  transmission  of  impulses  of  painful  sen- 
sil)ility  are  shown  diagramniatically  in  Fig.  117. 


280 


INTRODUCTION    TO    NEUROLOGY 


It  may  be  assumed  that  pain  and  an  avoiding  reaction  and  pleasure  and 
a  seeking  reaction  have  come  to  be  instinctively  associated  by  natural 
selection  or  other  biological  agencies  because  this  is  an  adaptation  useful 
to  the  organism.  No  separate  neurons  would  be  required  for  the  trans- 
mission and  analysis  of  painful  stimuli  in  their  simpler  forms.  A  peri- 
pheral neuron,  say,  of  the  pressure  sense,  if  excited  by  the  optimum 
stimulus  will  transmit  the  appropriate  nervous  impulse  to  the  tactile 
centers  of  the  thalamus  and  cerebral  cortex.  But  the  peripheral  sensory 
neurons  branch  widely  within  the  spinal  cord  and  there  effect  very  di- 


To  the  thalamus 


Fasciculus  proprius 
Spinal  lemniscus 


Spinal  nerve 


Fig.  117. — Diagram  of  the  pathways  of  painful  sensibility  in  the  spinal 
cord.  The  spinal  lemniscus  is  the  dominant  path  in  the  human  body,  and 
the  fasciculus  proprius  is  the  dominant  path  in  other  mammals. 


verse  types  of  connection  (see  Fig.  61,  p.  145);  and  supernormal  or  maxi- 
mal stimulation  of  the  end-organ  may  excite  so  strong  a  nervous  dis- 
charge as  to  overflow  the  tactile  pathway  in  the  spinal  cord  by  overcoming 
the  synaptic  resistance  of  certain  other  collateral  pathways  with  a  higher 
threshold  than  those  of  the  tactile  path,  thus  exciting  to  function  the 
pathway  for  painful  sensibility  with  its  own  central  connection  in  the 
thalamus  (Fig.  118,  A). 

In  the  course  of  the  further  differentiation  of  the  cutaneous  receptors, 


PAIN    AND    PLEASURE 


281 


the  peripheral  fiber  of  the  sensory  neuron  may  branch  and  effect  connec- 
tion with  two  types  of  sense  organs,  one  organ  (a  tactile  spot)  with  a  low 
threshold  for  pressure  stimuli  whose  nervous  impulses  are  so  attuned  as  to 
discharge  centrally  at  the  first  synapse  into  the  tactile  tract,  and  another 
organ  differently  constructed  (a  pain  spot)  which  generates  nervous  im- 
pulses so  attuned  as  to  discharge  centrally  into  the  pain  tract  (Fig.  118, 
B).  In  a  still  more  highly  elaborated  system  two  separate  peripheral 
neurons  may  be  present  to  serve  these  functions,  which  are  distinct 
throughout  (Fig.  118,  C).  The  experiments  of  Ranson  (see  p.  263) 
seem  to  indicate  that  in  cats  the  fibers  of  the  peripheral  nerve  roots  which 
conduct  painful  sensibility  are  distinct,  as  illustrated  in  this  third  case, 
and  that  centrally  these  fibers  (which  are  unmyelinated)  form  a  special 
tract  in  the  fasciculus  dorso-lateralis  (Lissauer's  tract)  and  terminate  in 
the  gelatinous  substance  of  Rolando  (see  Fig.  58,  p.  140). 


pain  path 
Tactile  path 
sKin 


spinal  cord 


pain  path 
tactile  path 


pain 


spinal  lemniscus- 


a,  pain 

b,  touch 


pfflinspot 


nacUe 
spot 


spinal  cord 


A.  ■■'"  B.  ^'^'"  C. 

Fig.  118. — Three  diagrams  to  illustrate  various  ways  in  which  the  nerves  of 

painful  sensibility  may  be  associated  with  those  of  other  sensory  functions. 

All  three  of  these  methods  of  pain  transmission  and  analysis  may  be 
present  in  the  spinal  nerves;  but  by  whatever  pathway  the  pain  impulses 
reach  the  spinal  cord,  in  the  human  body  those  which  are  destined  to 
excite  consciousness  of  pain  as  a  localizable  sensation  are  immediately 
filtered  off  from  the  other  sensory  qualities  with  which  they  may  be 
associated  and  assembled  in  a  pathway  of  their  own,  which  remains 
distinct  from  this  time  forth.  Within  the  spinal  cord  and  brain  stem 
these  pain  impulses,  especially  those  resulting  from  supernormal  stimula- 
tion, also  effect  short  reflex  connections  with  the  adjacent  motor  centers 
for  quick  avoiding  reflexes,  and  these  may  not  be  associated  with  the 
spinal  lemniscus,  but  with  the  more  diffuse  pain  path  in  the  fasciculus 
proprius. 

The  terminus  of  the  ascending  pain  tract  is  related  within  the 
thalamus  very  differently  from  those  of  the  pathways  for  tac- 
tile and  thermal  sensitivity.  The  latter  impulses  are  in  part 
transmitted  to  the  motor  centers  of  the  thalamus  for  intrinsic 
thalamic  reflexes,  but  chiefly  pass  forward  after  a  synapse  in 
the  thalamus  through  the  internal  capsule  to  the  somesthetic 
centers  of  the  cerebral  cortex.  Head  is  of  the  opinion  that 
the  painful  impulses  do  not  reach  the  cortex  at  all  in  their 


282  INTRODUCTION  TO  NEUROLOGY 

simple  elementary  form,  but  that  the  painful  sensations  are 
essentially  thalamic  (cf.  p.  182). 

Lesions  of  the  lateral  and  ventral  nuclei  of  the  thalamus  in- 
volving the  termini  of  the  medial  lemniscus,  but  leaving  the 
geniculate  bodies  and  pulvinar  and  the  medial  and  anterior 
nuclei  intact,  result  in  the  more  or  less  complete  loss  of  super- 
ficial sensation  of  the  opposite  side  of  the  body,  with  still  more 
profound  disturbance  of  deep  sensibility  and  the  postural 
sensations,  together  with  an  exaggeration  of  painful  sensi- 
bility. The  modifications  of  pain  and  affective  sensibility 
are  regarded  by  Head  and  Holmes  as  the  most  constant  and 
characteristic  features  of  lesions  of  the  lateral  zone  of  the 
thalamus.  Acute,  persistent,  paroxysmal  pains  are  always 
present,  often  intolerable  and  yielding  to  no  analgesic  treat- 
ment. There  is  also  a  tendency  to  react  excessively  to  un- 
pleasant stimuli  This  is  not  necessarily  associated  with  a 
lowering  of  the  threshold  of  stimulation.  Deep  pressure 
is  especially  important  here.  The  pain  does  not  develop 
gradually  out  of  the  general  sensation,  but  appears  explosively. 
This  pain  has  some  factors  to  which  the  normal  half  of  the 
body  is  not  particularly  susceptible.  Thermal,  visceral,  and 
other  sense  qualities  are  similarly  affected.  Tickling  is  very 
unpleasant  on  the  affected  side.  The  pleasurable  aspect  of 
moderate  heat  is  accentuated  on  the  affected  side,  yet  the 
threshold  for  heat  is  never  lowered.  Not  only  does  the  side  of 
the  body  involved  react  more  vigorously  to  an  affective  element 
of  a  stimulus,  but  an  overreaction  can  also  be  evoked  by  purely 
mental  states.  The  manifestations  of  this  increased  suscepti- 
bility to  states  of  pleasure  and  pain  are  strictly  unilateral. 
Associated  with  this  overreaction  to  painful  stimuli  some  loss 
of  general  sensation  will  always  be  manifest  on  the  affected 
side  of  the  body. 

Pure  cortical  lesions  cause  no  change  in  the  threshold  to  pain, 
nor  is  there  the  exaggerated  affective  quality  characteristic  of 
thalamic  lesions.  Head  and  Holmes  assume  that  both  the 
thalamus  and  the  cortex  are  concerned  in  conscious  activity. 
They  say: 

"The  most  remarkable  feature  in  that  group  of  thalamic  cases  with 
which  we  have  dealt  in  this  work  is  not  the  loss  of  sensation,  but  an  exces- 


TAIN    AND    PLEASURE  2<S;> 

sivo  response  to  affeelive  stiiDuli.  This  positive  effect,  an  acfual  over- 
loading of  sensation  witli  feeling  tone,  was  present  in  all  our  24  eases  of 
tliis  elass."  This  effect  is  interpreted  as  due  to  the  release  of  the  inhibi- 
tory or  regulatory  influence  of  the  cortex  arising  from  the  destruction  of 
the  asc(Miding  and  descending  fibers  1ir1\\  een  the  thalamus  and  the  cortex, 
thus  isolating  (he  thalanuis  and  allowing  it  to  act  to  excess.  Tliesc; 
authors  aild,  since  "the  affective  states  can  be  increased  when  the  thala- 
mus is  freed  from  cortical  control,  we  may  conclude  that  the  activity  of 
the  essential  thalamic  center  is  mainly  occupied  with  the  affective  side  of 
sensation."  "This  conclusion  is  strengthened  by  the  fact  that  station- 
ary cortical  lesions,  however  extensive,  wliich  cause  no  convulsions  or 
other  signs  of  irritation  and  shock,  produce  no  effect  on  sensibility  to  pain. 
Destruction  of  the  cortex  alone  does  not  disturb  the  threshold  for  the 
painful  or  uncomfortable  aspects  of  sensation." 

Some  recent  experiments  by  Cannon  have  revealed  a  very 
intimate  relation  between  emotion  and  some  of  the  ductless 
glands.  The  suprarenal  (or  adrenal)  glands,  situated  above 
the  kidneys,  secrete  and  pour  into  the  blood  a  remarkable 
substance  known  as  adrenalin  or  epinephrin.  This  substance 
exerts  upon  structures  which  are  innervated  by  sympathetic 
nerves  the  same  effects  as  are  produced  by  impulses  passing 
along  those  nerves.  The  glands  may  themselves  be  excited 
to  activity  by  nervous  impulses  passing  out  through  the 
sympathetic  nerves.  Cannon  has  shown  that  the  emotions 
of  fear,  rage,  and  pain  excite  these  glands  to  activity  and  cause 
the  secretion  of  adrenalin.  The  blood  of  a  caged  cat  which  has 
been  tormented  by  the  barking  of  a  dog  will  show  an  increased 
percentage  of  adrenalin.  The  addition  of  adrenalin  to  the 
blood  has  the  further  effect  of  causing  liberation  of  sugar 
from  the  liver  into  the  blood  to  such  an  extent  that  sugar  may 
appear  in  the  urine  (glycosuria) ;  and  sugar  is  known  to  be  the 
most  available  form  in  which  energy  can  be  quickly  supplied 
to  tissues  which  have  been  exhausted  by  exercise.  Adrenalin 
will  in  this  and  other  ways  act  as  an  antidote  to  muscular 
fatigue.  It  also  renders  more  rapid  the  coagulation  of  the 
blood 

If  a  muscle  is  fatigued,  the  threshold  of  irritability  rises.  It 
may  rise  as  much  as  600  per  cent.,  but  the  average  increase  is 
approximately  200  per  cent.  If  the  fatigued  muscle  is  allowed 
to  rest,  the  former  irritability  is  gradually  regained,  though  two 
hours  may  pass  before  the  recovery  is  complete.  If  a  small 
dose  of  adrenalin  is  administered  intravenously,  or  the  adrenal 


284  INTRODUCTION   TO    NEUROLOGY 

glands  are  stimulated  to  secrete,  Cannon  has  found  that  the 
former  irritability  of  the  fatigued  muscle  may  be  recovered 
within  three  minutes.  In  this  way  adrenal  secretion  may 
largely  restore  efficiency  after  fatigue. 

Fear  and  anger — as  well  as  worry  and  distress — are  attended 
by  cessation  of  the  contractions  of  the  stomach  and  intestines. 
These  mental  states  also  reduce  or  temporarily  aboUsh  the 
secretion  of  gastric  juice.  Adrenalin  injected  into  the  body 
has  the  same  effect.  Besides  checking  the  functions  of  the 
aHmentary  canal,  adrenalin  drives  out  the  blood  which,  during 
digestive  activity,  floods  the  abdominal  viscera.  This  blood 
flows  all  the  more  rapidly  and  abundantly  through  the  heart, 
the  lungs,  the  central  nervous  system,  and  the  limbs. 

Cannon  epitomizes  the  account  from  which  the  above  has 
been  condensed  in  these  words:  "The  emotional  reactions 
above  described  may  each  be  interpreted,  therefore,  as  making 
the  organism  more  efficient  in  the  struggle  which  fear  or  rage  or 
pain  may  involve.  And  that  organism  which,  with  the  aid  of 
adrenal  secretion,  best  mobilizes  its  sugar,  lessens  its  muscular 
fatigue,  sends  its  blood  to  the  vitally  important  organs,  and 
provides  against  serious  hemorrhage,  will  stand  the  best  chance 
of  surviving  in  the- struggle  for  existence."  It  should  be 
added  that  some  of  Cannon's  observations  have  not  been 
confirmed  by  more  recent  experiments  of  Stewart  and  others 
and  some  of  his  conclusions  are  controverted. 

The  preceding  account  includes  a  summary  of  some  of  the 
most  securely  established  facts  regarding  the  peripheral  and 
central  nervous  mechanisms  of  painful  impressions  and  the 
physiology  of  the  emotions,  together  with  a  theoretical  interpre- 
tation of  the  apparently  twofold  nature  of  pain  as  a  specific 
sensation  and  as  a  component  of  the  general  affective  state  of 
the  bodv  as  a  whole.  The  more  general  questions  concerning 
the  physiological  processes  related  with  pleasurable  and  un- 
pleasant experience  and  the  affective  life  in  general  are  still 
more  difficult  of  analysis.  It  seems  probable  that  pain, 
unpleasant  and  pleasurable  feelings,  emotion,  and,  in  short, 
the  entire  affective  life  are  very  intimately  related  on  the 
neurological  side. 

Many  physiological  theories  of  pleasure-pain  have  been  elaborated,  for 


PAIN    AND    PLEASURE  285 

the  most  part  on  very  slender  observational  grounds.  It  has  been  sug- 
gested that  the  flexor  movements  of  the  body  are  associated  with  pain,  the 
extensor  movements  ■n'ith  pleasure;  that  constructive  metaboUsm  is 
pleasurable,  destructive  metabolism  disagreeable;  that  heightened 
nervous  discharge  is  pleasurable,  and  the  reveree  (some  form  of  inhibition 
or  of  antagonistic  contraction)  is  unpleasant.  Some  hold  that  pain  and 
unpleasantness  or  disagreeableness  are  different  in  degree  only,  not  in 
kind.  Others  regard  pain  as  a  true  sensation,  but  disagreeableness  and 
pleasure  (aftective  experience)  as  belonging  to  a  different  category  which 
is  non-sensory.  In  the  latter  case  the  affective  experience  may  be  neuro- 
logically  related  in  some  way  with  the  various  sensations  (including  pain) 
or  the  affective  experience  and  sensations  may  be  independent  variables 
with  separate  cerebral  mechanisms.  None  of  these  hypotheses,  or  many 
others  wliich  might  be  mentioned,  are  competent  to  explain  satisfactorily 
all  of  the  known  facts,  though  strong  arguments  can  be  adduced  in 
support  of  each  of  them. 

Our  own  view  is  that  pleasurable  and  unpleasant  experiences  are  not 
true  sensations,  that  in  the  history  of  the  psychogenesis  of  primitive 
animals  a  diffuse  unlocalized  affective  experience  of  well-being  or  malaise 
probably  antedated  anytliing  so  clearly  analyzed  as  a  sensation  with 
specific  external  reference,  and  that,  parallel  ■ndth  the  differentiation  of 
true  sensations  of  touch,  temperature,  and  so  on  in  consciousness,  pam 
sensations  emerged  out  of  the  diffuse  aff'ective  experience  and  took  their 
place  among  the  other  sense  qualities.  An  essential  condition  for  the 
appearance  in  consciousness  of  a  definite  sensation  hke  touch  or  vision  is 
the  difi"erentiation  in  the  nervous  system  of  a  system  of  localized  tracts 
and  centers  related  to  this  fimction,  and  in  the  human  body  such  loeaUzed 
tracts  and  centers  seem  to  be  present  for  pain.  Pain,  therefore,  con- 
sidered psychologically  and  neurologically,  is  a  sensation,  and  a  different 
neurological  mechanism  for  unpleasantness  and  pleasantness  must  be 
sought.    To  this  problem  we  shall  next  turn  our  attention. 

We  have  seen  above  that  it  is  possible  to  frame  a  neurological  hypothe- 
sis which  allows  a  given  peripheral  sensory  neuron  to  be  conceived  as 
transmitting,  say,  a  ta(^tual  impression  from  the  skin  and  also  a  painful 
impression  from  the  same  or  a  different  end-organ.  Upon  reaching  the 
spinal  cord  the  nervous  impidses  of  the  tactual  series  may  pass  through 
one  tj-pe  of  spinal  s\-napse  to  the  spinal  lemniscus,  and  finally  reach  the 
tactual  center  of  the  cerebral  cortex,  and  the  nervous  impulses  of  the 
painful  series  may  be  drawn  off'  through  a  second  system  of  synapses  for 
transmission  through  a  distinct  system  of  central  pathway's.  Attention 
has  also  been  called  to  the  fact  that  the  specific  pain  nerves  and  central 
paths  may  have  been  developed  by  a  process  of  the  further  dift'erentiation 
of  separate  neurons  with  chfferent  peripheral  and  central  connections  for 
these  two  functions.  But  what  of  the  pleasurable  qualities  which  seem 
similarly  to  be  associated  with  some  sensory  impulses? 

The  simplest  view  seems  to  the  writer  to  be  that  the  normal  activity  of 
the  body  within  physiologicallimits  is  intrinsicalh'  pleasurable,  so  far  as  it 
comes  into  consciousness  at  all.  There  is  a  simple  joy  of  living  for  its  own 
sake,  and  the  more  productive  the  life  is,  within  well-defined  physiological 
limits  of  fatigue,  good  health,  and  diversified  types  of  reaction,  the  greater 
the  happiness.  The  expenditure  of  energy  wnthin  these  physiological 
limits  is  pleasurable  per  se  except  in  so  far  as  various  psychological  factors 
enter  to  disturb  the  simple  natural  physiological  expression  of  bodily 


28(3  INTRODUCTION    TO    NEUROLOGY 

activity.  Such  disturbing  factors  are  anxiety,  want,  rebellion  against 
compulsory  service,  and  unrelieved  routine.  The  expenditure  of  intel- 
ligently directed  nervous  energy  along  lines  of  fruitful  endeavor  is  prob- 
ably the  highest  type  of  pleasure  known  to  mankind. 

A  certain  spontaneity  of  action,  as  Huxley  long  ago  pointed  out,  is 
characteristic  of  all  life  and  its  natural  expression  gives  rise  to  a  primeval 
joy  of  living.  Life  in  its  fulness  is  more  than  immediate  reaction  to 
stimuli.  As  Max  Eastman  says  in  a  delightful  essay  (The  Will  to  Live, 
Jour.  Philos.,  Psych.,  Sci.  Methods,  vol  xiv,  1917,  pp.  102-107),  "We  are 
not  merely  trying  to  adapt  ourselves  in  order  to  stay  alive,  but  we  are 
trying  also  even  more  energetically  to  live.  Everything  we  do  and  think 
is  not  a  reaction;  a  great  deal  of  it  is  ^ction.  .  .  .  Life  interflows  with 
reality  in  full  circles.  We  do  things  not  only  because  we  have  a  sensa- 
tion, but  also  in  order  to  make  a  sensation.  And  so  do  the  most  ele- 
mentary organisms.  Any  rubber  ball  can  react,  but  it  requires  life  to 
act.  And  life  does  act.  It  seeks  experience."  This  primitive  reaching 
out  of  the  organism  for  experience  leads  up  to  curiosity,  the  unquenchable 
impulse  toward  scientific  discovery,  and  the  divine  fire  of  creative  artistic 
genius.  The  evolutionary  factor  operating  here  is  more  than  self-pres- 
ervation; it  is  self-realization  and  fulfilment. 

And  it  should  be  borne  in  mind  that  the  normal  activities  of  the  body 
are  all  combined  into  adaptive  systems,  that  is,  they  are  directed  toward 
the  accomplishment  of  definite  ends  and  not  directed  at  random.  Even 
in  instinctive  activities  of  the  invariable  or  innate  type,  though  there  may 
be  no  consciousness  of  the  end  to  be  attained,  the  actions  are  not  satisfy- 
ing to  the  animal  unless  they  follow  in  the  predetermined  adaptive  se- 
quence (p.  64).  The  play  of  both  men  and  other  animals  is  likewise  al- 
ways correlated  around  some  definite  physiological  motive.  And  it  is 
even  more  conspicuously  true  that  the  intelligently  directed  activities  are 
unsatisfying  unless  they  attain,  or  at  least  approximate  to,  some  par- 
ticular end.  Stated  in  other  words,  it  is  not  the  activity  which  is  pleasur- 
able, so  much  as  the  accomplishment,  or,  in  the  case  of  delayed  reactions, 
the  hope  of  accomplishment. 

The  normal  discharge,  then,  of  definitely  elaborated  nervous  circuits 
resulting  in  free  unrestrained  activity  is  pleasurable,  in  so  far  as  the  reac- 
tion comes  into  consciousness  at  all  (of  course,  a  large  proportion  of  such 
reactions  are  strictly  reflex  and  have  no  conscious  significance).  Con- 
versely, the  impediment  to  such  discharge,  no  matter  what  the  occasion, 
results  in  a  stasis  in  the  nerve  centers,  the  summation  of  stimuli  and  the 
development  of  a  situation  of  unrelieved  nervous  tension  which  is  un- 
pleasant until  the  tension  is  relieved  by  the  appropriate  adaptive  reac- 
tion. Such  a  stasis  may  be  brought  about  bj^  a  conflict  of  two  sensory 
impulses  for  the  same  final  common  path  (see  p.  61),  by  the  dilemma  oc- 
casioned by  the  necessity  for  discrimination  in  an  association  center 
between  two  or  more  possible  final  paths,  by  fatigue,  auto-intoxication, 
or  other  physiological  states  which  lower  the  efficiency  of  the  central 
mechanism,  and  by  a  variety  of  other  causes.  The  unrelieved  summation 
of  stimuli  in  the  nerve  centers,  involving  stasis,  tension,  and  interference 
with  free  discharge  of  nervous  energy,  gives  a  feeling  of  unpleasantness 
which  in  turn  (in  the  higher  types  of  conscious  reaction  at  least)  serves 
as  a  stimulus  to  other  associated  nerve  centers  to  participate  in  the 
reaction  until  finally  the  appropriate  avenue  for  an  adaptive  response  is 
opened  and  the  situation. is  relieved.     With  the  release  of  the  tension  and 


PAIN    XN\)    PLKASUKE  2<S7 

free  discluirgc,  llu;  feeliiif^  tone  cluuiges  to  ;i  distinctly  plcasural)l(!  (|ii;ilifv 
(see  C.  L.  Ilcrrick,  1910). 

The  fact  that  tiic  primitive  pain  path  in  the  sjMnal  cord  seems  to  follow 
a  rather  diffnscly  arranged  system  of  fibers  in  the  fasciculus  proprius,  fre- 
quently interrupted  l)y  synapses  in  tiie  gray  matter  (Fig.  117)  with  corre- 
spondingly high  resistance  to  nervous  conduction,  is  perhaps  correlated 
with  this  general  and  diffuse  quality  of  unpleasantness. 

Now,  pain  as  a  distinct  and  localizable  sensation  has  not  been  involved 
in  the  situation  described  in  the  preceding  paragraphs.  Pain,  considered 
as  a  distinct  sensation,  was,  however,  born  out  of  this  situation  or  differ- 
entiated from  it.  Certain  sensational  elements  which  have  a  high  protec- 
tive value  for  the  organism  are  naturally  most  often  involved  in  such  a 
situation.  These  are  warning  calls,  and  usually  necessitate  an  interrup- 
tion of  the  ordinary  business  of  life  which  may  be  in  process  at  the  time  the 
danger  threatens.  The  free  flow  of  ordinary  sensori-motor  activity  is 
abruptly  checked,  and  the  organism  suddenly  stops  and  makes  the  neces- 
sary readjustment  as  quickly  as  may  be.  In  the  interest  of  increasing  the 
rapidity  of  this  avoiding  reaction,  which,  of  course,  is  frequently  of  vital 
importance,  the  pathways  of  the  exteroceptive  pain  reactions  are  well 
developed  and  segregated  from  the  more  diffuse  and  poorly  organized 
affective  apparatus  which  we  have  just  been  considering.  Thus  arose 
pain  nerves  (if  sucli  exist  separately)  and  the  pain  tract  of  the  spinal  cord 
(whose  anatomical  distinctness  seems  well  established),  and  also  perhaps 
a  special  mechanism  for  painful  reactions  in  the  thalamus.  Sherrington 
has  given  a  graphic  statement  of  the  probable  history  of  this  process  in 
the  following  words  (Schafer's  Physiology,  vol.  ii,  p.  974): 

"The  facility  of  path  of  these  motor  reflexes  colligated  to  pain  hints  at 
their  antiquity,  or  at  their  having  been  formed  by  some  neural  method 
particularly  able  to,  as  it  were,  make  a  good  road.  Each  reaction  that 
employs  a  neural  path  seems  to  smooth  it  by  sheer  act  of  travel.  This  is 
true  even  of  slight  impulses — light  traffic — and  more  true  of  heavy. 
Pain  reactions  are  to  be  regarded  as  very  heavy  traffic.  Their  impres- 
sions summate  with  peculiar  ease,  take  correspondingly  long  periods  to 
subside,  and,  to  judge  by  their  inertia,  move  generally  masses  of  neural 
material  relatively  great.  Such  impressions  might  wear  a  road  with 
quite  especial  speed.  Many  spinal  reflexes  imply,  so  to  say,  well-worn 
habits  based  on  ancient  pain  reactions.  One  is  almost  emboldened  to 
figuratively  imagine  them  as  connate  memories  of  the  spinal  cord.  The 
majority  of  them  seem  to  be  protective  reactions  that  in  organisms  of 
high  neural  type  are  accompanied  by  'pain.'  " 

But  even  in  this  case  the  apparatus  for  pain  is  incapable  of  acting  as 
rapidly  as  are  those  of  some  other  sensations.  If  a  sensitive  corn  on  the 
foot  is  struck  a  sharp  blow,  one  will  often  feel  a  verj^  distinct  tactile  sensa- 
tion an  appreciable  interval  before  the  painful  quality  is  perceived,  the 
latter,  however,  soon  welling  up  into  consciousness  and  obscuring  the  tac- 
tile quality  entirely.  This  is  an  illustration  of  the  fact  that  even  the 
highly  protective  exteroceptive  painful  stimuli  pass  through  a  mechanism 
of  slower  reaction  time  than  the  primary  exteroceptive  sensations  with 
which  they  may  l)e  associated. 

We  cannot  here  enter  into  a  full  discussion  of  the  larger  questions  cen- 
tering about  the  physiological  correlates  of  the  higher  affective  life,  the 
emotions  and  esthetics.  It  has  often  be?n  pointed  out  that  the  conscious 
processes  resulting  from  exteroceptive  stimulation  tend  to  be  directed 


288  INTRODUCTION    TO    NEUROLOGY     ' 

outward,  the  attention  being  focussed  on  the  external  objects  giving  rise 
to  the  stimuU  with  a  minimum  of  personal  reference.  The  deep  sensa- 
tions, both  of  the  proprioceptive  and  the  interoceptive  group,  on  the 
other  hand,  have  a  less  clearly  defined  local  sign  and  the  mental  attitude 
toward  them  is  not  one  of  outwardly  directed  attention  to  the  source  of 
the  stimulus,  but  rather  a  change  in  the  subjective  state  and  an  alteration 
of  the  general  feeling  tone  of  the  body  as  a  whole.  Under  ordinary  cir- 
cumstances the  visceral  afferent  and  other  deep  nervous  impulses  do  not 
come  into  clear  consciousness  separately,  but  in  the  aggregate  these  com- 
plexes (often  termed  as  a  whole  common  sensation)  profoundly  modify 
the  general  mental  attitude  and  equilibrium.  The  generalized  feelings 
of  both  the  pleasurable  and  the  painful  type  share  this  subjective  refer- 
ence with  the  common  sensations.  They  are  very  important  factors  in 
that  sensory  continuum  which  lies  at  the  basis  of  the  maintenance  of 
personal  identitj''  which  the  older  psychologists  sometimes  called  the 
empirical  ego.  Only  the  pains  associated  with  the  sharply  localized 
cutaneous  sensation  qualities  with  a  high  adaptive  value  as  warning  signs 
of  external  danger  have  a  distinct  peripheral  reference,  and  even  this  is 
less  clearly  defined  than  that  of  the  accompanying  sensations  of  pressure, 
and  so  forth.  The  deep  pains  are  imperfectly  localized  and  have  more  of 
the  general  subjective  reference  which  has  just  been  mentioned,  and  all  of 
the  pleasurable  qualities  are  of  this  type. 

The  simpler  affective  types  of  experience,  accordingly,  seem  to  be  most 
intimately  associated  with  the  "common  sensation"  complex,  especially 
with  the  visceral  sensation  components  of  this  complex.  From  this  it  has 
been  argued  that  the  coarser  emotions,  as  well  as  the  elementary  feelings, 
are  the  direct  expression  in  consciousness  of  these  visceral  activities,  that 
the  well-known  visceral  changes  associated  with  the  emotions  are  no  t  the 
results,  but  the  causes  of  the  emotions  (Lange  and  James).  This  hy- 
pothesis has  been  attacked  experimentally  by  Sherrington  (see  The  Integ- 
rative Action  of  the  Nervous  System,  1906,  p.  260),  who  found  that  cutting 
the  afferent  sympathetic  fibers  from  the  abdominal  viscera  in  dogs  made 
no  apparent  difference  in  the  emotional  reactions  of  the  animals;  but  the 
experiments  are  not  very  convincing,  and  the  question  is  probably  too 
complex  for  solution  by  so  simple  means  as  those  here  emplo3^ed. 

The  probability  is  that  we  have  here  a  circular  type  of  reaction.  The 
initial  visceral  afferent  impulses,  being  heavily  charged  with  affective 
qualities  and  with  a  minimum  of  objective  reference,  excite  within  the 
brain,  probably  in  the  medial  thalamic  nuclei,  a  general  non-localized 
pleasurable  or  unpleasant  feeling,  a  feeling  of  well-being  or  malaise,  as  the 
case  may  be.  These  thalamic  receptive  centers  are  in  very  intimate  rela- 
tion with  the  visceral  efferent  systems  of  the  hypothalamus  and  a  reflex 
response  in  the  viscera  follows — a  typical  organic  circuit.  So  long  as  this 
circuit  involves  only  the  viscera  and  their  thalamic  centers  the  peripheral 
reference  will  be  at  a  minimum,  and  the  feeling  remains  an  unlocalized 
change  in  the  affective  consciousness. 

The  higher  emotional  and  esthetic  activities  are  so  charged  with  intel- 
lectual content  also  as  to  require  the  participation  of  the  association  cen- 
ters of  the  cerebral  cortex.  But  no  pleasure-pain  centers  are  known  in 
the  cortex  and  the  evidence  at  present  available  seems  to  negative  the 
presence  of  such  centers.  The  agreeable  or  disagreeable  components  of 
the  higher  emotional  processes  are  very  probably  due  to  the  colligation  of 
thalamic  activities  with  cortical  associational  processes.    In  case  these 


PAIN    AND    PLEASURE  280 

emotional  or  esthetic  processes  are  of  cortical  origin,  that  is,  excited  in 
the  first  instance  by  the  activity  of  cortical  associational  centers,  their 
affective  content  niaj-  be  due  to  the  involvement  of  the  subcortical  pleas- 
ure-pain apparatus  in  the  associational  process,  and  this  apparatus  would, 
as  above  described,  generate  efferent  impulses  from  the  related  visceral 
centers,  thus  causing  the  characteristic  visceral  movements,  which  in  turn 
would  reinforce  the  visceral  activities  of  the  brain  centers,  and  thus  by  a 
"back-stroke"  action  strengthen  the  emotional  content  of  the  primary 
associational  complex.  Thus  the  completion  of  the  circular  reaction 
may  reinforce  the  affective  consciousness  so  long  as  it  is  operative. 

That  pleasure  is  correlated  with  free  discharge  of  nervous  energy  is  sug- 
gested further  bj^  the  fact  that  in  most  of  the  pleasurable  emotions  and 
sentiments  there  is  present  a  large  factor  of  recall  of  previous  experiences. 
The  esthetic  enjoyment  of  a  given  situation  is  in  large  measure  propor- 
tional to  the  wealth  of  associated  memories  incorporated  within  it,  especi- 
all}'  when  these  are  recombined  into  new  patterns.  The  pleasure  expe- 
rienced in  listening  to  a  complicated  musical  production  like  a  symphony 
may  be  enhanced  many  fold  after  one  has  become  thoroughly  familiar 
with  it,  and  still  more  so  if  the  listener  has  himself  played  it  or  parts  of  it. 

In  concluding  this  discussion  of  pleasure-pain  we  quote  the  following 
paragraph  from  Sherrington's  account  of  Cutaneous  Sensations,  already 
referred  to  (Schafer's  Physiology,  1900,  vol.  ii,  p.  1000): 

"Affective  tone  is  an  attribute  of  all  sensation,  and  among  the  attribute 
tones  of  skin  sensation  is  skin-pain.  Affective  tone  inheres  more  intenseh- 
in  senses  which  refer  to  the  body  than  in  those  which  refer  to  the  environ- 
ment, that  is,  it  is  strongest  in  the  non-projicient  senses.  It  is,  therefore, 
strong  in  the  cutaneous  senses,  and  in  them  is  inversely  as  their  proji- 
cience,  therefore  least  in  touch  spots,  more  in  thermal  spots,  most  in  the  so- 
called 'pain-spots.'  .  .  .  Stimuli  evoking  skin-pain  are  broadly  such  as 
injure  or  threaten  injury  to  the  skin;  the  skin  may  be  said  to  have  gone  far 
toward  developing  a  special  sense  of  its  own  injuries.  The  central  con- 
ducting path  concerned  with  these  skin  feelings  seems  a  side-path  into 
which  the  impressions  from  the  various  skin  spots  embouch  with  various 
ease,  those  from  the  'pain  spots'  especially  easih'.  The  physiological 
reactions  connected  with  this  side-path  are  characterized  by  tondencj-  to 
'summation,'  tendencj'  to  'collateral  irradiation,'  slow  culmination,  and 
slow  subsidence.  The.v  often  involve  with  their  own  activity  that  of 
adjacent  sensory  channels  (associate  pains,  referred  pains),  and  almost 
invariably  of  motor  centers  of  visceral,  facial,  and  other  muscles  of 
expression  (emotional  discharge)." 

Our  own  view  is  in  harmony  with  that  expressed  in  this  paragraph  ex- 
cept that,  while  we  recognize  that  sensations  in  general  have  an  affective 
tone,  we  do  not  consider  that  affective  experience  is  to  be  regarded  as 
essentially  an  attribute  or  quale  of  sensation.  These  are  independent 
variables  which  are,  however,  usually  intimately  associated.  Each  has 
its  own  mechanism.  The  mechanism  of  every  sensation  is  a  localizable 
system  of  tracts  and  centers  as  expounded  in  the  preceding  chapters. 
The  mechanism  of  the  affective  experience  is  a  more  general  neural 
attitude  or  physiological  phase,  intimately  bound  up  with  the  visceral 
reactions  peripherally  and  integrated  centrally  in  the  thalamus. 

Summary. — In  the  human  organism  pain  appears  to  be  a  true 
sensation  with  its  own  receptors,  probably  with  independent 

19 


290  INTRODUCTION    TO    NEUROLOGY 

peripheral  neurons  (in  some  cases  at  least),  and  certainly  with 
well  localized  conduction  paths  and  cerebral  centers,  these  cen- 
ters being  thalamic  and  not  cortical.  Pain  appears  to  Ix^ 
closely  related  neurologically  with  feelings  of  unpleasantness 
and  pleasantness,  and  these,  in  turn,  with  the  higher  emotions 
and  the  affective  life  in  general.  The  intellectual  elements  in 
the  higher  emotions  and  sentiments  are,  of  course,  cortical. 
Nearly  all  cases  of  affective  experience  probably  involve  a 
highly  complex  interaction  of  cortical  and  subcortical  activities. 
Pleasantness  and  unpleasantness  are  not  regarded  simply  as 
attributes  of  specific  sensory  processes  in  any  case,  but  rather 
as  a  mode  of  reaction  or  physiological  attitude  of  the  whole 
nervous  system  intimately  bound  up  with  certain  visceral 
reactions  of  a  protective  sort  whose  central  control  is  effected 
in  the  ventral  and  medial  parts  of  the  thalamus.  These  parts 
of  the  thalamus  form,  accordingly,  the  chief  integrating  center 
of  the  nervous  reactions  involved  in  purely  affective  experience. 
This  mechanism  is  phylogenetically  very  old,  and  in  lower 
vertebrates  which  lack  the  cerebral  cortex  it  is  adequate  to 
direct  avoiding  reactions  to  noxious  stimuli  and  seeking  reac- 
tions to  beneficial  stimuli.  With  the  appearance  of  the  cortex 
in  vertebrate  evolution  these  thalamic  centers  became  inti- 
mately connected  with  the  association  centers  of  the  cerebral 
hemispheres,  and  an  intelligent  analysis  of  the  feelings  of 
unpleasantness  and  pleasantness  became  possible.  As  a  final 
step  in  the  development  of  the  protective  apparatus  the  pe- 
ripheral nerves  of  painful  sensibility,  with  their  own  specific 
conduction  paths  and  centers,  were  differentiated,  and  pain 
takes  its  place  among  the  other  exteroceptive  senses.  But 
even  in  man  the  thalamic  and  visceral  mechanisms  of  affective 
experience  are  preserved  and  give  a  characteristic  organic 
background  to  the  entire  conscious  life.  In  the  normal 
man  these  mechanisms  may  function  with  a  minimum  of  cor- 
tical control,  giving  the  general  feeling  tone  of  well-being  or 
malaise,  or  they  may  be  tied  up  with  the  most  complex  coitical 
processes,  thus  entering  into  the  fabric  of  the  higher  sentiments 
and  affections  and  becoming  important  factors  in  shaping 
human  conduct. 


PAIN    AND    PLEASURE  291 


Literature 


Cannon,  W.  B.  1915.  Bodily  Changes  in  Pain,  Hunger,  Fear,  and 
jciage,  New  York,  311  pages. 

Capps,  J.  A.  1911.  An  Experimental  Study  of  the  Pain  Sense  in  the 
Pleural  Membranes,  Arch.  Internal  Medicine,  vol.  viii,  pp.  717-733. 

Dearborn,  G.  V.  N.     1916.     The  Influence  of  Joy.     Boston. 

Head,  H.,  and  Holmes,  G.  1911.  Sensory  Disturbances  from  Cere- 
bral Lesions,  Brain,  vol.  xxxiv,  pp.  109-254. 

Head,  H.,  and  Thompson,  T.  1906.  The  Grouping  of  the  Afferent 
Impulses  Within  the  Spinal  Cord,  Brain,  vol.  xxix,  p.  537. 

Herrick,  C.  L.  1910.  The  Summation-irradiation  Theory  of  Pleas- 
ure-pain. In  The  Metaphysics  of  a  Naturalist,  Bull.  Denison  University 
Scientific  Laboratories,  vol.  xv. 

Holmes,  S.  J.  1910.  Pleasure,  Pain,  and  the  Beginnings  of  Intelli- 
gence, Jour.  Comp.  Neur.,  vol.  xx,.pp.  145-164. 

James,  W.  1890.  The  Principles  of  Psychology,  New  York,  vol.  ii,  pp. 
442-485. 

— .     1894.     The  Physical  Basis  of  Emotions,  Psych.  Rev.,  vol.  i,  p.  516. 

Karplus,  J.  P.,  and  Kreidl,  A.  1914.  Ein  Beitrag  zur  Kenntnis  der 
Sc^hmerzleitung  im  Riickenmark,  nach  gleichzeitigen  Durchschneidungen 
beider  Riickenmarkshalften  in  verschiedenen  Hohenbei  Katzen,  Pfluger's 
Archiv,  Bd.  158,  pp.  275-287. 

Lange,  C.  1887.  L^eber  Gemilthsbewegungen.  Eine  Psycho-physio- 
logische  Studie,  Leipzig. 

Meyer,  Max.  1908.  The  Nervous  Correlate  of  Pleasantness  and  Un- 
pleasantness, Psych.  Rev.,  vol.  xv,  pp.  201-216,  292-322. 

Sherrington,  C.  S.  1900.  Cutaneous  Sensations,  in  Schafer's  Physi- 
ology, vol.  ii,  pp.  965-1001. 

— .     1906.     The  Integrative  Action  of  the  Nervous  System,  New  York. 

Stewart,  G  .N.  and  Rogoff,  J.  M.  1916.  The  Influence  of  Certain 
Factors,  Especially  Emotional  Disturbances,  on  the  Epinephrin  Content 
of  the  Adrenals,  Jour.  Exp.  Med.,  vol.  xxiv,   pp.  709-738. 

Watson,  J.  B.  1913.  Image  and  Affection  in  Behavior,  Jour.  Philos. 
Psych.  Sci.  Methods,  vol.  x,  pp.  421-428. 


CHAPTER  XIX 
THE    STRUCTURE    OF    THE    CEREBRAL    CORTEX 

The  preceding  pages  have  included  a  brief  chapter  on  some 
of  the  general  biological  principles  underlying  the  differentia- 
tion of  the  structure  and  functions  of  the  nervous  system,  some 
general  characteristics  of  the  nervous  tissues,  a  brief  survey 
of  the  structure  of  the  various  great  divisions  of  the  nervous 
system,  and  finally  an  analysis  of  the  more  important  sensori- 
motor reflex  circuits.  Nearly  all  of  the  mechanisms  hitherto 
considered  are  concerned  with  the  innate  invariable  types  of 
response  represented  in  the  reflex  and  instinctive  life  of  the 
organism  (p.  31).  In  the  higher  mammals,  and  especially  in 
man,  the  individually  acquired  relatively  variable  types  of 
action,  particularly  those  which  are  consciously  performed, 
require  the  cooperation  of  the  cerebral  cortex,  and  the  following 
chapters  will  be  devoted  to  a  consideration  of  the  cortex,  its 
structure,  functions,  evolution,  and  biological  significance. 

We  have  already  commented  (p.  239)  on  the  fact  that 
the  cerebral  cortex  appeared  later  in  vertebrate  evolution  than 
most  of  the  other  parts  of  the  brain,  and  that  in  general  it 
serves  the  individually  acquired  and  intelligent  functions,  in 
contrast  with  the  brain  stem  and  cerebellum,  which  contain  the 
apparatus  for  the  innate  activities  of  the  reflex  type.  The 
primary  reflex  centers  of  the  brain  stem  and  cerebellum,  ac- 
cordingly, are  sometimes  called  the  old  brain  (palseencephalon, 
see  Fig.  45,  p.  123),  while  the  cerebral  cortex  and  those  parts 
of  the  brain  stem  which  develop  as  subsidiary  to  the  cortex 
(such  as  the  neothalamus,  p.  179)  are  called  the  new  brain 
(neencephalon).^ 

1  A  review  of  the  evolution  of  the  brain  and  the  phylogenetic  origin  of 
the  cerebral  cortex  would  he  beyond  the  limits  of  this  work,  for  the  litera- 
ture upon  this  subject  is  very  extensive.     The  following  papers  may  be 

292 


TUlO    .STHUt-'TUllE    OF    THK    CJOltKHKAI.    ('OHIKX 


'2\rA 


In  the  embryologic  development  of  the  human  brain  the  ecre- 
l)ral  hemispheres  grow  out  as  lateral  pouches  from  the  anterior 
end  of  the  nenial  tube  (Figs.  46-54,  pp.  125-130).  Thpse 
pouches  are  hollow  and  the  cavities  within  them  are  the  lateral 
ventricles  (also  called  the  first  and  second  ventricles),  each  of 


Olfactory  nerve 
Olfactory  bulb 
Lateral  ventricle 
Corpus  striatum 
Lamina  terminalis 
Interventricular  foramen 
Third  ventri:'lc 
Optic  lobe 
Cerebellum 
Fourth  ventricle 


Fig.  119. — Diagrammatic  representation  of  an  amphibian  brain  from 
which  the  roof  of  the  thalamus  and  cerebral  hemisphere  has  been  dissected 
off  on  the  right  side,  exposing  the  third  and  the  lateral  ventricles  and  the 
interventricular  foramen  (foramen  of  Monro.)  The  membranous  roof  of  the 
fourth  ventricle  has  also  been  removed. 


which  communicates  with  the  third  ventricle  of  the  thalamus 
by  a  narrow  opening,  the  interventricular  foramen  or  foramen 
of  Monro. 

In  a  simply  organized  brain  like  that  of  the  frog  (Fig.  119) 


consulted  in  the  present  context.  (See  also  the  bibliographies  on  pp. 
174,  187,  248.) 

Herhick,  C.  Judson.  1910.  The  Evolution  of  Intelligence  and  Its 
Organs,  Science,  N.  S.,  vol.  xxxi,  pp.  7-18. 

Smfth,  G.  Elliot.  1910.  The  Arris  and  Gale  Lectures  on  Some  Prob- 
lems Relating  to  the  Evolution  of  the  Brain,  The  Lancet  for  Januarv  1,  15, 
and  22,  1910. 

Smith,  G.  Elliot.  1912.  The  Evolution  of  Man,  Report  of  the  An- 
thropological Section  of  the  British  Assoc,  for  the  Advancement  of 
Scienc-e,  Dundee  Meeting.  Printed  also  in  \ature  (London)  for  Sept.  26, 
1912,  and  in  the  Smithsonian  Report  (Washington)  for  1912,  pp.  553-572. 


294  INTRODUCTION  TO  NEUROLOGY 

the  olfactory  bulb  forms  the  anterior  end  of  each  cerebral 
hemisphere,  behind  which  the  massive  wall  contains  ventrally 
the  basal  olfactory  centers  (p.  243),  laterally  the  corpus 
striatum  (p,  183),  and  dorsally  the  cerebral  cortex  or  pallium 
(which  has  been  removed  on  the  right  side  of  Fig.  119).  In 
the  human  brain  the  cerebral  cortex  is  so  greatly  enlarged 
that  it  overlaps  all  other  structures  of  the  hemisphere. 

The  anterior  end  of  the  early  neural  tube  is  an  epithelial 
plate,  the  terminal  plate  or  lamina  terminalis,  which  forms  the 
anterior  wall  of  the  third  ventricle  in  the  median  plane.  The 
position  of  this  plate  is  unchanged  throughout  all  subsequent 
stages  of  development  (Figs.  46-51,  pp.  125-128,  and  Fig.  119), 
though  the  cerebral  hemispheres  grow  forward  on  each  side 
of  it,  so  that  in  the  adult  brain  it  lies  deeply  buried  at  the 
bottom  of  the  great  longitudinal  fissure  which  separates  the 
hemispheres. 

The  reflex  centers  of  the  two  sides  of  the  spinal  cord  and 
brain  stem  are  connected  by  transverse  bands  of  fibers  known 
as  comynissures,  for  the  facilitation  of  bilateral  adjustments. 
There  is  an  extensive  series  of  ventral  commissures  crossing 
below  the  ventricle  in  the  floor  of  the  midbrain,  medulla 
oblongata,  and  spinal  cord,  and  several  smaller  dorsal  com- 
missures are  found  above  the  ventricle.  In  the  diencephalon 
there  is  a  large  ventral  commissure  associated  with  the  optic 
chiasma,  and  a  dorsal  commissure,  the  superior  or  habenular 
commissure,  connecting  the  habenular  bodies  of  the  epithala- 
mus.  The  basal  parts  of  the  cerebral  hemispheres  are  con- 
nected by  the  anterior  commissure,  whose  fibers  cross  in  the 
lamina  terminalis  (Fig.  78,  p.  180),  and  there  are  two  large 
commissures  which  connect  the  cerebral  cortex  of  the  two 
hemispheres.  One  of  these,  the  corpus  callosum  (Figs.  52, 
p.  128,  and  78,  p.  180),  connects  the  non-olfactory  cortex 
(neopallium,  p.  241),  the  other  one,  the  hippocampal  com- 
missure, connects  the  olfactory  cortex  (hippocampus).  The 
fibers  of  the  hippocampal  commissure  lie  under  the  posterior 
end  of  the  corpus  callosum  in  close  relation  with  the  fimbria 
(Figs.  78,  p.  180,  and  80,  p.  185). 

In  the  smaller  mammals  the  cerebral  cortex  is  smooth,  but  in 
the  larger  forms  it  is  more  or  less  wrinkled,  so  that  the  surface 


THE  STRUCTURE  OF  THE  CEREBRAL  CORTEX 


295 


is  marked  by  gyri  or  convolutions  separated  by  sulci  or  fissures. 
A  more  highly  convoluted  cortical  pattern  is  found  in  large 
animals  than  in  smaller  ones  of  closely  related  species,  and  in 
animals  high  in  the  zoological  scale  than  in  lower  species;  but 
the  factors  which  have  determined  this  pattern  in  each  indi- 
vidual species  are  very  complex  (see  Kappers,  1913  and  ]914). 
The  primary  factor  in  the  higher  mammals  has  undoubtedly 
been  the  great  increase  in  the  superficial  area  of  cortical  gray 
matter  without  a  corresponding  enlargement  of  the  skull. 

The  human  cerebral  cortex  is  somewhat  arbitrarily  divided 
into  frontal,  temporal,  parietal,  and  occipital  lobes  (Fig.  120). 


OCCIPITAL 
LOBE 


Fig.   120. — The  lateral  aspect  of  the  human  brain,  illustrating  the  houndarins 
of  the  lobes  of  the  cerebral  cortex  (cf.  Fig.  54). 


These  lobes  have  no  special  functional  significance,  but  are  dis- 
tinguished merely  for  convenience  of  topographic  description. 
Some  of  the  more  important  gyri  and  sulci  are  named  on  Figs. 
52  and  54  (pp.  128  and  130).  Between  the  temporal  and 
frontal  lobes  and  under  the  lower  end  of  the  lateral  or  Sylvian 
fissure  is  a  buried  convolution,  the  island  of  Reil  (insula), 
which  is  seen  in  section  in  Figs.  79  and  80  (pp.  181  and  185). 
The  cortical  lobules  which  cover  the  insula  are  called  opercula 
(Fig.  54,  p.  130). 

The  walls  of  the  cerebral  hemispheres  in  the  cortical  region 
are  very  thick,  the  greater  part  of  this  thickness  being  occupied 
by  white  matter  composed  of  nerve-fibers  which  effect  various 
types  of  connection  with  the  nem-ons  of  the  cerebral  cortex. 
The  cortex  itself  is  composed  of  gray  matter  and  is  relatively 


296 


INTRODUCTION    TO    NEUROLOGY 


thin,  its  inner  border  being  marked  by  a  broken  line  in  Figs. 
79  and  80.  The  subcortical  white  matter  contains  three  chief 
classes  of  fibers:  (1)  Corona  radiata  fibers  which  connect  the 
cortex  with  the  brain  stem  (Figs.  79,  80),  Most  of  these 
fibers  pass  through  the  internal  capsule  and  comprise  the 
sensory  and  motor  projection  fibers  (pp.  180-186);  (2)  commis- 
sural fibers  of  the  corpus  callosum  and  hippocampal  commis- 
sure (Figs.  79,  80) ;  (3)  association  fibers,  which  connect  different 


str.  term, 
f.  I.  s. 


tunc' 


f.  occ.fr.  inf- 


Fig.  121. — Diagram  illustrating  some  of  the  chief  association  tracts  of 
the  cerebral  hemisphere,  seen  as  projected  upon  the  median  surface  of  the 
right  hemisphere:  cin.,  cingulum;  f.l.i.,  fasciculus  longitudinalis  inferior; 
/.Z.S.,  fasciculus  longitudinalis  superior  ;/.occ./r.m/.,  fasciculus  occipito-frontalis 
inferior;  f.p.,  arcuate  fibers;  f.tr.oc,  fasciculus  transversus  occipitalis;  /.  unc, 
fasciculus  vincinatus;  str.  term.,  stria  terminalis. 


parts  of  the  cerebral  cortex  of  each  hemisphere.  Some  of  these 
fibers  are  very  short,  passing  between  adjacent  gyri  (arcuate 
fibers,  or  fibrse  proprise,  /.p.,  Fig.  121);  others  are  very  long 
fibers,  forming  compact  fascicles  which  can  easily  be  dissected 
out  and  which  connect  the  important  association  centers  of 
the  cortex.  All  parts  of  the  cerebral  cortex  are  directly  or 
indirectly  connected  with  all  other  parts  by  these  association 
fibers,  so  that  no  region  can  be  regarded  as  the  exclusive  seat 
of  any  particular  cortical  function. 

The  human  cortex  varies  in  thickness  in  different  regions 


THE  STRUCTURE  OF  THE  CEREBRAL  CORTEX 


297 


from  about  4  mm.  in  the  motor  area  to  less  than  half  that 
thickness  in  some  other  parts.  When  cut  across  and  examined 
in  the  fresh  condition  it  shows  alternate  bands  of  light  and 
dark  gray,  whose  arrangement  varies  in  different  parts  of  the 
hemisphere.     The  light  bands  are  composed  of  myelinated 


Millimetres 


'/-.PAR  A  SUP.rRON.         INF.rROH. 


«L:i 


SUP.PAR.B  CALLOS/iLA     ORBITAL  INTERNED. FROM  FROM  B  PRECEHT.B  POSTCEHT 


■  II       lit       Efl 


tfi  STRI.4TA     AREA  PARASTR    AREA  PERISTR.       PAR.OCC.  SUP.  TEMP.  HESCHLSTENr:    PAWDENTATE 


s    mi    m\\    «ii 


Fig.  122. — Drawings  showing  the  naked-eye  appearances  of  sections  of  the 
fresh  cerebral  cortex  in  different  regions.  (After  Elliot  Smith  from  Quain's 
Anatomy.) 

The  areas  are  named  according  to  charts  of  the  cortex  published  by  Elliot 
Smith  (1907;  see  also  Quain's  Anatomy,  11th  ed.,  vol.  iii,  Part  I,  p.  373). 
The  equivalent  regions  of  Brodmann's  charts  (Figs.  130,  131,  p.  305)  are 
approximately  as  follows: 

Area  parastr.  =  area  18  in  part;  Area  peristr.  =  areas  18,  19  in  part 
Area  striata  =  area  17;  Callosal  A  =  areas  21,  23  in  part;  Fron.  B.  =  lower 
parts  of  areas  8,  9,  upper  part  of  area  46;  =  HenschVs  temp.  —  area  41  in  part 
Inf.  fron.  =  areas  44  (anterior  part),  45;  Inf.  par.  A  =  area  39;  Inf.  temp.  = 
area  20;  Intermed.  fron.  =  anterior  border  of  lower  lateral  part  of  area  6 
Mid.  temp.  =  area  21;  Orbital  =  area  47;  Paradentate  =  area  36;  Par.  occ.  = 
midlateral  part  of  area  19;  Polar  temp.  =  area  38;  Postcent.  =  areas  1,  2,  3 
Precent.  A  =  posterior  part  of  area  4;  Precent.  B  =  anterior  part  of  area  4 
Prefron.  =  area  11;  Sup.  fron.  =  upper  part  of  areas  6,  8,  9;  Sup.  par.  A  = 
area  7;  Sup.  par.  B  =  area  5;  Supraspl.  (area  parasplenialis)  =  areas  29,  30 
Sup.  temp.   =  areas  22,  41,  42. 


fibers  which  run  parallel  with  the  surface.  There  are  typically 
two  of  these  light  bands,  in  addition  to  the  thin  superficial 
white  plexiform  layer,  the  outer  and  inner  stripes  of  Baillarger 
(Figs.  122  and  127).  In  the  visual  projection  center  (Figs. 
130,  131,  area  ]7)  the  outer  stripe  of  Baillarger  is  greatly 
thickened  by  the  optic  projection  fibers,  and  here  it  is  some- 


298 


INTRODUCTION    TO    NEUROLOGY 


times  called  the  line  of  Gennari.     The  portion  of  cortex  ex- 
hibiting the  line  of  Gennari  is  called  the  area  striata  (Figs.  130, 
131,   p.  305,   area  17  and  in  modified  form  areas  18  and  19). 
The  most  characteristic  neurons  of  the  cortex  are  pj-ramidal 


Fig.  123.  —  Diagraniiuatic  illu:<tratioQ  of  the  arrangement  of  neurons  in 
the  cerebral  cortex  as  revealed  by  the  Golgi  method.  The  fig\ire  is  copied 
from  Obersteiner  and  the  layers  are  numbered  difTerently  than  in  Brodmann'.s 
scheme.  Fig.  127.  Oberstoiner's  layer  III  includes  layers  III.  IV.  and  V  of 
Brodmann.  The  arrows  indicate  the  direction  of  nervous  conduction,  and 
the  axons  of  the  neurons  are  marked  by  a  cross,  X :  o/.,  layer  of  superficial 
neuroglia  cells;  m.  beginningof  the  layer  of  white  matter:  12. 13.  14.  andlo  mark 
neuroglia  (glia)  cells;  the  other  numbers  designate  different  t>-pes  of  neurons. 

in  shape,  with  the  apex  directed  toward  the  outer  surface  of  the 
brain  and  prolonged  to  form  the  principal  dendrite.  Smaller 
dendrites  arise  from  other  parts  of  the  cell  body,  and  the  a.\on 
arising  from  the  l)ase  of  the  cell  body  is  directed  inward  into 
the  white  matter  (  Fijrs.  7,  S.  pp.  43,  4o).     The  cortex  contains, 


THK    STRUCTITRE    OF   THE    CEREBRAL    COltTEX  299 


Fig.  124. — Section  from  the  cerebral  cortex  of  a  human  infant  from  the 
postcentral  gyrus  (gyrus  centralis  posterior),  with  the  neurons  impregnated 
by  the  method  of  Golgi.  The  figure  is  taken  from  Ramon  y  Cajal's  Histology 
of  the  Central  Nervous  System,  and  the  layers  are  numbered  according  to 
his  system.  Layer  1  corresponds  to  Brodmann's  first  layer  (Fig.  127) ;  layer 
2,  to  his  second  layer;  layers  3  and  4,  to  his  third  layer;  layer  5,  to  his  fourth 
layer;  layer  6,  to  his  fifth  layer;  and  layer  7,  to  his  sixth  layer. 


300 


INTRODUCTION    TO    NEUROLOGY 


Fig.  125. — Section  of  the  human  cerebral  cortex  from  the  precentral  gyrus 
(gyrus  centralis  anterior),  illustrating  the  free  endings  of  the  incoming  fibers. 
This  region  contains  a  large  number  of  cells  similar  to  those  shown  in  Fig. 
124;  but  none  of  the  cells  were  stained  in  this  preparation,  which  was  pre- 
pared by  the  method  of  Golgi.  At  a  and  h  are  seen  the  terminal  arborization 
of  two  individual  fibers.  At  5  is  a  dense  entanglement  of  such  terminal 
arborizations  around  the  cell  bodies  of  the  pyramidal  neurons  of  layer  3 
(Fig.  124).  C,  D,  and  E  illustrate  horizontally  directed  nerve-fibers,  from 
which  the  terminal  arborizations  shown  in  the  upper  part  of  the  figure  arise. 
(After  Ramon  y  Cajal.) 


THE  STRUCTURE  OF  THE  CEREBRAL  CORTEX 


301 


moreover,  many  other  types  of  neurons,  some  of  irregular 
shape  (polymorphic  or  multiform  cells)  and  many  whose 
axons  are  short  and  ramify  close  to  the  cell  body  without 
leaving  the  cortex  itself  (Fig.  9,  p.  45).  These  type  II  neurons 
probably  assist  in  the  summation  and  irradiation  of  stimuli 
(see  p.  107).  Some  other  types  of  neurons  are  shown  in 
Fig.  123. 


Fig.  126.— Section  of  the  human  cerebral  cortex  from  the  precentra 
gyrus,  illustrating  the  details  of  the  terminal  arborizations  of  the  incoming 
fibers  (a)  in  the  form  of  a  closely  woven  feltwork  of  fibers  {b,  c,  d)  around  the 
cell  bodies  of  the  large  pyramidal  cells  of  the  cortex.  The  cells  themselves 
are  not  stained  in  the  preparation,  but  their  outlines  are  clearly  indicated 
by  the  pericellular  basket-work  by  which  they  are  enveloped.  (After  Ramon 
y  Cajal.) 


Figure  124  illustrates  a  typical  arrangement  of  the  neurons  in 
the  postcentral  gyrus  (g.  centralis  posterior  of  Fig.  54,  p.  130). 
Most  of  the  neurons  here  shown  send  their  axons  inward  to 
participate  in  the  formation  of  the  white  matter  and  may  dis- 
charge their  nervous  impulses  into  remote  parts  of  the  brain. 
The  endings  of  the  afferent  nerve-fibers  which  effect  synaptic 
connection  with  the  neurons  here  shown  form  a  dense  entangle- 
ment of  fine  unmyelinated  fibers  between  the  dendrites  of  these 
neurons.     These  afferent  fibers  are  not  included  in  Fig.  124; 


302 


INTRODUCTION    TO    NEUROLOGY 


Fig.  12V. — Diagram  of  Xne  arrangement  of  the  layers  of  cells  and  mye- 
linated nerve-fibers  in  the  cerebral  cortex,  according  to  Brodmann.  At  the 
left  of  the  figure  is  shown  the  arrangement  of  cells  as  shown  by  the  Golgi 
method,  in  the  middle  their  arrangement  as  shown  liy  Nissl's  method,  and 
at  the  right,  the  arrangement  of  nerve-fibers  as  shown  by  Weigert's  method. 
/.  Lamina  zonalis,  or  plexiform  layer,  containing  tangential  nerve- 
fibers. 

//.  Lamina  granularis  externa,  or  layer  of  small  pyramidal  cells. 
III.  Lamina  pyramidalis,  or  layer  of  niediiim  and  large  pyramidal  cells. 


THE    JSTRliCTliltlO    Ol'     rilK    ('KK10J5KAL    I'OKTEX  308 

one  of  them  is  shown  in  l-'ig.  123  and  they  arc  (hawii  separately 
in  Fip;.  125  as  they  appear  in  the  precential  {;yrus  (gyrus  cen- 
tralis anterior  of  Fig.  54).  These  afferent  fibei's  may  be 
•cither  sensory  piojeetion  fibers  or  association  fibers  from  other 
parts  of  the  cortex.  The  synapses  between  these  incoming 
fibers  and  the  neurons  of  the  cortex  among  which  they  end  are 
of  various  types.  Many  of  the  afferent  fibers  end  in  the  outei- 
most  layer  of  the  cortex  (layer  1  of  Figs.  123  and  124)  among 
the  dendrites  of  the  pyramidal  cells  which  are  here  widely 
expanded  (see  Fig.  8,  p.  45) ;  others  end  in  dense  arborizations 
which  closely  envelop  the  bodies  of  the  pyramidal  cells  (Fig. 
126).  Still  others  twdne  around  the  dendrites  for  their  entire 
length.  The  dendrites  of  the  pyramidal  cells  are  very  rough 
and  thorny,  and  these  thorns  are  supposed  by  some  to  be  the 
points  where  the  actual  synaptic  connections  are  effected. 

Besides  the  lamination  caused  by  the  bands  of  tangential 
nerve-fibers  already  referred  to,  the  cell  bodies  themselves  are 
arranged  in  layers  whose  pattern  varies  in  different  parts  of  the 
cortex.  Neurologists  enumerate  these  layers  differently. 
Brodmann,  who  has  studied  this  question  very  exhaustively, 
enumerates  six  primary  layers  which  in  most  parts  of  the  cortex 
are  arranged  essentially  as  shown  in  the  accompanjdng  dia- 
gram (Fig.  127).  The  six  layers  here  recognized  are  present  in 
most  but  not  in  all  parts  of  the  cortex.  In  the  different  regions 
one  or  more  of  these  layers  may  be  reduced,  enlarged,  or 
subdivided;  and  on  the  basis  of  these  differences  the  entire 
cortex  has  been  mapped  out  into  areas,  each  of  which  is  de- 
fined by  the  arrangement  of  the  layers  of  cortical  cells  and 
fibers. 

Brodmann  (Figs.  128,  129)  divides  the  cerebral  hemisphere 
into  eleven  general  regions,  which  he  says  are  recognizable  more 
or  less  clearly  throughout  the  entire  group  of  mammals. 
These  are: 

IV.  Lamina  granulans  interna,  or  inner  granular  layer,  containing  the 
medullated  fibers  of  the  external  line  of  Baillarger  (in  the  visual  area  called 
the  stripe  of  Cicnnari). 

V.  Lamina  ganglionaris,  or  layer  of  large  cells,  containing  in  the  motor 
area  the  giant  pyramidal  cells  or  Betz  cells,  from  which  the  fibers  of  the 
pyramidal  tract  arise,  and  containing  in  most  areas  the  medullated  fibers  of 
the  internal  line  of  Baillarger. 

VI.  Lamina  multiformis,  or  layer  of  polymorphic  cells. 


304 


INTRODUCTION    TO    NEUROLOGY 


Fig.  128. — The  chief  regions  of  the  human  cerebral  cortex  as  determined 
by  Brodmann  from  the  study  of  the  structural  arrangements  of  the  layers  of 
cells  and  fibers,  seen  from  the  left  side. 


Fig.  129. — The  chief  regions  of  the  cortex,  seen  from  the  median  side. 


THE    .STRUCTURE    OF    THE    CEREBRAL    CORTEX 


80;-) 


Fig.  130. — The  detailed  subdivisions  of  the  cortical  regions  shown  in  Fig. 
128  as  determined  by  Brodmann,  seen  from  the  left  side.  Each  area  or 
field  which  is  here  designated  by  a  number  and  conventional  symbols  has  a 
distinctive  lamination  of  its  cells  and  fibers. 


Fig.   131. — The  same  brain  shown  in  Fig,   130,  seen  from  the  median  side. 
20 


306  INTRODUCTION  TO  NEUROLOGY 

1.  Regio  postcentralis  (tactile  region). 

2.  Regio  precentralis  (motor  region). 

3.  Regio  frontalis  (frontal  association  center). 

4.  Regio  insularis  (insula). 

5.  Regio  parietalis  (parietal  association  center). 

6.  Regio  temporalis  (auditory  region). 

7.  Regio  occipitalis  (visual  region). 

8.  Regio  cingularis  (supracallosal  part  of  limbic  lobe). 


Fig.  132. — Arrangement  of  nerve  cell  bodies  in  the  cortex  of  the  post- 
central gyrus  (Field  3  of  Brodmann,  cf.  Fig.  130).  The  cells  are  arranged 
in  the  six  typical  layers  shown  in  Fig.  127.      (After  Brodmann.) 

9.  Regio  retrosplenialis  (postcallosal  part  of  limbic  lobe). 

10.  Regio  hippocampica  (gyrus  hippocampi  and  hippocampus). 

11.  Regio  olfactoria  (uncus,  amygdala,  tuberculum  olfactorium). 

In  the  list  as  here  given  Brodmann's  names  of  the  regions  are 
given,  and  in  parenthesis  is  added  a  brief  description  of  each 
region.  Regions  8,  9,  10,  and  11  are  all  concerned  with  the 
olfactory  reactions,  though  region  8  only  to  a  small  extent. 
Region  11  is  only  in  part  cortical  (the  uncus);  the  other  parts 
of  this  region  are  subcortical  olfactory  centers.  The  specific 
sensory  and  motor  projection  centers  (see  p.  180)  lie  within 
their  respective  regions,  as  designated,  but  they  do  not  occupy 
the  whole  of  their  regions.  On  the  basis  of  the  arrangement  of 
their  cells  and  fibers  these  regions  are  further  subdivided  by 


THE  STRUCTURE  OF  THE  CEREBRAL  CORTEX      307 

Brodmanii  into  upward  of  50  areas  or  fields,  as  shown  in  Figs. 
130  and  131.  The  areas  are  less  uniformly  developed  in 
different  animals  than  are  the  general  regions,  though  many 
of  them  are  very  constantly  present.     In  the  human  brain  the 


U:i--:^'S?^^^?^ijfj::'Mi^^^ 


Fig.  133. — Arrangement  of  cells  in  the  cortex  of  the  precentrai  gj^rus  (Field 
4,  Fig.  130).  This  is  the  motor  cortex;  here  the  fourth,  or  internal  granular, 
layer  is  absent.  In  the  fifth  layer  are  seen  the  giant  pyramidal  cells  of  Betz, 
from  which  the  fibers  of  the  p>Tamidal  tract  arise.     (After  Brodmann.) 

arrangements  of  nerve  cells  in  some  of  these  areas  are  seen  in 
Figs.  132,  133,  and  134. 

Bolton,  Campbell,  Ramon  y  Cajal,  Vogt,  Elliot  Smith,  and 
many  others  have  investigated  the  lamination  of  the  cerebral 
cortex  in  man  and  other  mammals,  and  many  charts  similar  to 


308  INTRODUCTION  TO  NEUROLOGY 

those  here  presented  have  been  published.  The  conclusions 
reached  by  these  authors  do  not  agree  in  all  respects  (particu- 
larly in  the  number  of  areas  separately  recognized  and  the 
nomenclature  of  the  layers  of  cells  and  fibers  in  the  various 
regions) ;  nevertheless  there  is  a  sufficiently  close  general  agree- 
ment to  make  it  evident  that  there  is  a  definite  structural 


IV 


Fig.  134. — Arrangement  of  cells  in  the  cortex  of  the  visual  area.  The 
arrow  marks  the  transition  between  the  calcarine  type  of  cortex  on  the  right 
(Field  17,  Fig.  131)  and  the  adjacent  occipital  cortex  on  the  left.  The  latter 
is  (somewhat  obscurely)  six  layered,  but  in  the  calcarine  area  the  fourth,  or 
internal  granular  layer  is  greatly  thickened.      (After  Brodmann.) 

pattern  which  is  characteristic  of  the  several  cortical  regions 
in  each  species  of  mammals,  and  that  this  pattern  is  broadly 
similar  in  all  of  the  higher  members  of  this  group  of  animals. 
Data  derived  from  physiological  experiments  made  on  dogs, 
apes  and  bther  animals,  and  from  the  study  of  pathological  hu- 
man brains  have  shown  also  that  the  difference  in  structural 
pattern  of  the  cortical  areas  is  correlated  with  differences  in 


Vlb 


THE  STRUCTURIO  OP  THE  CEREBRAL  CORTEX      '.^0^ 

llu^  functions  performed  by  them.     To  these  functional  ques- 
tions our  attention  will  next  be  directed. 

Summary. — The  cerebral  cortex  is  the  organ  of  the  highest 
individually  modifiable  functions,  particularly  those  of  the 
intellectual  life.  It  matures  late  in  both  phylogenetic  and  indi- 
vidual development,  and  therefore  has  been  called  the  neen- 
cephalon.  In  early  developmental  stages  it  forms  the  roof  of 
the  lateral  ventricle  of  each  cerebral  hemisphere,  but  in  the 
adult  human  brain  it  is  so  enlarged  as  to  envelop  most  other 
parts  of  the  hemisphere.  The  cortex  of  the  two  hemispheres  is 
connected  by  commissural  fibers  in  the  corpus  callosum  and  the 
hippocampal  commissure.  The  various  regions  of  each  hemi- 
sphere are  connected  by  a  complex  web  of  association  fibers, 
and  some  parts  of  the  cortex  are  connected  with  subcortical 
regions  by  projection  fibers.  The  sensory  projection  fibers 
discharge  among  the  neurons  of  the  sensory  projection  centers, 
and  the  motor  projection  fibers  arise  from  neurons  of  the 
motor  projection  centers.  The  intervening  association  centers 
are  connected  with  the  projection  centers  and  with  each  other 
by  very  intricate  systems  of  association  fibers.  The  cortex 
is  laminated  by  bands  of  horizontally  arranged  nerve-fibers 
and  by  an  arrangement  of  its  cells  in  layers.  The  pattern  of 
this  lamination  varies  in  different  regions,  and  charts  of  these 
structurally  defined  regions  are  found  to  show  a  general 
correlation  with  the  functionally  defined  areas  as  physiologic- 
ally and  pathologically  determined. 

Literature 

Bolton,  J.  S.  1910.  A  Contribution  to  the  Localization  of  Cerebral 
Function,  Based  on  the  Clinico -pathological  Study  of  Mental  Disease, 
Brain,  vol.  xxxiii.  Part  129,  pp.  26-148. 

Bolton,  J.  S.,  and  Moves,  J.  M.  1912.  The  Cytoarchitecture  of  the 
Cerebral  Cortex  of  a  Human  Fetus  of  Eighteen  Weeks,  Brain,  vol.  xxxv. 

Brodmann,  K.  1907.  Die  Kortexgliederung  des  Menschen,  Jour,  f . 
Psychol,  u.  Neurol.,  Bd.  10. 

— .  1909.  Vergleichende  Lokalisationslehre  der  Grosshirnrinde. 
Leipzig. 

— .  1910.  Chapter  entitled,  Feinere  Anatoniio  des  Gro'sshirns,  in 
Lcwandowsky's  Handbuch  der  "Neurologie,  Bd.  1,  pp.  206-307. 

Campbell,  A.  W.  190.5.  Histological  Stxidies  on  the  Localization  of 
Cortical  F\mction,  Cambridge. 


310  INTRODUCTION  TO  NEUROLOGY 

Kappers,  C.  U.  a.  1913.  Cerebral  Localization  and  the  iSigiiiiicancf 
of  Sulci,  Proc.  XVII  Intern.  Congress  of  Medicine,  London. 

— .  1914.  Ueber  das  Rindenproblem  und  die  Tendenz  innerer  Hirn- 
teile  sich  durch  Oberflachen-Vermehrung  statt  Volumzunahme  zu  ver- 
grosseren,  Folia  Neuro-biologica,  Bd.  8,  pp.  507-531. 

Ram6n  y  Cajal.  1900-1906.  Studien  iiber  die  Hirnrinde  des  Men- 
schen,  Leipzig. 

Smith,  G.  Elliot.  1907.  A  New  Topographical  Survey  of  the  Human 
Cerebral  Cortex,  Jour.  Anat.  and  Physiol.,  vol.  xli. 

VoGT,  O.  1903.  Zur  anatomischen  Gliederung  des  Cortex  Cerebri, 
Jour.  f.  Psych,  u.  Neurol.,  Bd.  2. 

— .  1904.  Die  Markreifung  des  Kindergehirns  wahrend  der  ersten 
vier  Lebensmonate  und  ihre  methodologische  Bedeutung,  Jena. 


CHAPTER  XX 
THE  FUNCTIONS  OF  THE  CEREBRAL  CORTEX 

The  greatest  diversity  of  view  has  prevailed  and  still  prevails 
regarding  the  method  of  cortical  function.  That  the  cerebral 
cortex  is  concerned  in  some  way  with  the  higher  conscious  func- 
tions is  clearly  shown  by  a  large  body  of  experimental  and 
clinical  evidence. 

The  partial  or  complete  removal  of  both  cerebral  hemi- 
spheres has  been  accomplished  in  various  species  of  animals, 
from  fishes  to  apes,  and  the  changes  in  behavior  carefully 
studied.  In  fishes  and  frogs  the  behavior  is  but  little  modified, 
save  for  the  loss  of  the  sense  of  smell,  if  the  thalamus  is  left 
intact;  but  if  the  thalamus  also  is  destroyed,  the  animal 
loses  all  power  of  spontaneous  movement,  of  feeding  when 
hungry,  etc.,  though  it  will  still  react  to  some  strong  stimuli 
in  an  apparently  normal  manner.  The  fundamental  reflexes 
of  the  spinal  cord  and  brain  stem  are  but  little  modified  by  this 
operation  in  frogs,  save  for  the  disturbance  of  the  olfactory 
and  visual  functions.  The  recent  experiments  of  Burnett  have, 
moreover,  shown  that  frogs  in  which  the  cerebral  hemispheres 
alone  have  been  removed  are  somewhat  more  excitable  than 
normal  frogs  (probably  due  to  the  loss  of  cortical  inhibitions), 
and  that  simple  associations  easily  learned  by  normal  frogs 
are  in  this  case  impossible. 

In  the  dog  the  loss  of  the  cerebral  hemispheres  alone  leaves 
the  animal  in  a  state  of  profound  idiocy,  though  here  also  all 
of  the  primary  sensor i-motor  reflexes  (except  the  olfactorjO 
remain  if  the  thalamus  is  uninjured,  and  one  such  animal 
operated  on  by  Goltz  lived  for  eighteen  months.  During  this 
time,  however,  he  had  to  be  artificially  fed,  for  he  had  lost 
the  ability  to  recognize  food  when  set  before  him,  nor  did  he 
show  any  of  his  former  signs  of  intelligence.  (These  experi- 
ments are  summarized  in  Schafer's  Physiology,  vol.   ii,  pp. 

311 


312  INTRODUCTION  TO  NEUROLOGY 

698  &.,  to  which  the  reader  is  referred  for  references  to  the 
literature;  see  also  the  papers  by  Goltz,  Edinger,  and  Holmes, 
cited  in  the  appended  Bibliography.) 

More  recently  Karplus  and  Kreidl  (1914)  removed  one  or 
both  cerebral  hemispheres  from  a  number  of  rhesus  monkeys, 
none  of  which  survived  longer  than  twenty-six  days  after  the 
operation.  After  complete  removal  of  one  hemisphere  there 
were  few  enduring  symptoms  other  than  a  defect  of  vision 
(hemianopsia)  and  muscular  weakness  and  incoordination  in  the 
hand  of  the  side  opposite  the  injury.  Upon  removal  of  the  re- 
maining hemisphere  from  these  animals,  the  hand  partially 
paralyzed  by  the  first  operation  was  better  controlled  than  the 
other  hand;  but  movements  of  all  kinds  were  poorly  executed. 
Reflex  responses  followed  cutaneous,  optic  and  auditory 
stimulation.  The  monkeys '  were  unable  to  feed  themselves 
and  in  general  were  very  helpless,  apparently  being  reduced 
to  a  condition  of  profound  idiocy.  Cries  made  in  response 
to  painful  stimuli  were  not  accompanied  by  the  normal 
mimetic  movements. 

Edinger  and  Fischer  report  the  case  of  a  boy  who  lived  three 
years  and  nine  months,  whose  brain  when  examined  after  death 
showed  total  lack  of  the  cerebral  cortex  with  no  other  impor- 
tant defects.  In  this  boy  there  was  practically  no  development 
in  sensory  or  motor  power  or  in  intelligence  from  birth  to  the 
time  of  his  death.  The  infant  fed  when  put  to  the  breast,  but 
showed  no  signs  of  hunger,  thirst,  or  any  other  sensory  process. 
It  lay  in  a  profound  stupor  and  during  the  first  year  of  life  made 
no  spontaneous  movements  of  the  limbs.  Until  the  time  of 
death  there  was  little  change  from  this  condition,  save  for 
continual  crying  from  the  second  year  on.  This  case  shows 
that  the  reflex  functions  of  the  human  brain  stem  are  normally 
under  cortical  control  to  a  much  greater  extent  than  are  those 
of  any  of  the  lower  animals,  and  that  the  absence  of  the  cortex 
accordingly  involves  a  more  profound  disturbance  of  the  sub- 
cortical apparatus  (see  p.  140). 

About  a  hundred  years  ago  Gall  and  Spurzheim  examined 
the  brain,  form  of  skull,  and  physiognomy  of  many  persons 
whose  mental  characteristics  were  more  or  less  fully  known, 
and  reached  very  definite  conclusions  regarding  the  locahzation 


THE  FUNCTIONS  OF  'I'HE  CEREBRAL  CORTEX      'iVi 

within  the  brain  of  particular  mental  faculties,  such  as  benevo- 
lence, wit,  and  destructiveness;  they  claimed,  further,  that  the 
sizes  of  these  specific  parts  of  the  brain  (and  hence  their  relative 
physiological  importance)  can  be  determined  by  study  of  the 
external  configuration  of  the  skull.  Many  valuable  observa- 
tions were  accumulated  by  these  men  and  their  followers,  but 
the  data  Avere  so  uncritically  used  and  the  psj^chological  basis 
of  their  generalizations  was  so  faulty  that  the  alleged  science 
of  phrenology  which  they  founded  is  now  wholly  discredited 
and  is  professed  today  only  by  ignorant  charlatans. 

The  great  popularity  of  phrenology  fifty  years  and  more  ago 
grew  out  of  the  fact  that  it  served  to  give  a  pseudoscientific 
character  to  methods  of  reading  character,  and  hence  of  fore- 
casting the  future  formerl}-  claimed  by  astrologers  and  necro- 
mancers. JNIodern  psychology  recognizes  that  the  mind 
cannot  be  subdivided  into  any  such  distinct  "faculties" 
as  the  phrenologists  used,  and  modern  neurology  finds  no  basis 
for  the  sharply  defined  localization  of  these  or  any  other  mental 
functions,  in  the  sense  that  a  specific  cortical  area  is  the  exclu- 
sive organ  of  a  particular  mental  element. 

As  a  reaction  against  the  crude  theories  of  Gall  and  Spurz- 
heim  it  was  commonly  believed  up  to  the  year  1870  that  there 
is  no  definite  localization  of  functions  in  the  cerebral  cortex, 
but  that  the  cortex  functions  as  a  whole,  much  like  the  cere- 
bellar cortex,  with  no  clearly  defined  functional  areas.  This 
view  and  modifications  of  it  are  still  very  prevalent.  Goltz, 
who  succeeded  in  removing  all  of  both  cerebral  hemispheres 
from  several  dogs,  holds  tha.t  different  psychic  functions  are 
not  localizable  in  the  cortex,  but  that  removal  of  cortical  areas 
simply  diminishes  general  intelligence  in  proportion  to  the 
amount  of  cortex  removed.  Even  total  removal  of  the  cortex, 
in  his  opinion,  does  not  completely  destroy  consciousness. 
Many  physiologists  have,  on  the  other  hand,  taught  that 
particular  conscious  functions  are  localized  in  definite  cortical 
areas,  somewhat  after  the  fashion  of  a  refined  and  modernized 
phrenology,  and  this  view  is  very  prevalent  among  clinical 
neurologists. 

The  modern  period  of  study  of  cortical  functions  was  inaugu- 
rated by  a  chance  observation  on  the  battlefield.     During  the 


314  INTRODUCTION  TO  NEUROLOGY 

Franco-Prussian  war  an  army  surgeon,OPritsch,  while  operating 
on  a  wounded  soldier,  applied  the  galvanic  electric  current  to 
the  exposed  surface  of  the  brain  and  observed  a  twitching  of 
some  of  the  muscles.  This  was  followed  immediately  by 
experimental  researches  upon  the  electric  excitability  of  the 
cerebral  cortex  of  dogs,  the  first  results  of  which  were  published 
by  Fritsch  and  Hitzig  in  1870.  They  showed  that  there  are 
regions  in  the  vicinity  of  the  central  sulcus  (fissure  of  Rolando, 
cruciate  sulcus)  whose  excitation  in  the  living  animal  is 
followed  by  movements  of  definite  groups  of  muscles  on  the 
opposite  side  of  the  body. 

These  observations  have  been  followed  by  an  immense 
number  of  experimental  researches  on  various  animals  (the 
animals  being  anesthetized  during  the  experiments)  and 
clinico-pathological  studies  of  the  human  brain,  whose  corre- 
lation and  integration  have  proved  very  difficult.  The  most 
careful  studies  have,  however,  in  general  given  concordant 
results.  Without  attempting  a  summary  of  these  investi- 
gations here,  we  may  mention  the  recent  investigations  of 
Sherrington  on  the  chimpanzee,  whose  results  as  summarized 
on  Fig.  135  may  be  accepted  as  fully  in  accord  with  the  best 
previous  experimental  work,  with  the  anatomical  investiga- 
tions of  the  regional  differentiation  of  the  cortex,  and  with  the 
most  recent  clinical  studies.  The  corresponding  centers  of 
the  human  brain  are  seen  in  Fig.  136. 

The  electric  stimulation  of  each  one  of  the  shaded  regions 
of  Fig.  135  is  followed  by  the  contraction  of  a  particular  group 
of  muscles  on  the  opposite  side  of  the  body,  as  designated  on 
the  figure.  The  electrically  excitable  motor  cortex  is  of  two 
types,  marked  on  the  figure  by  stipple  and  vertical  cross- 
hatching  respectively.  Stimulation  of  the  latter  areas  in 
the  frontal  and  occipital  lobes  calls  forth  conjugate  move- 
ments of  the  eyes,  and  the  physiological  characteristics  of  these 
centers  are  very  difierent  from  those  of  the  centers  in  the 
precentral  gyrus,  which  are  shaded  with  stipple.  This  gyrus 
is  the  true  motor  projection  center,  and  a  comparison  of 
Figs.  135  and  136  with  Fig.  130  shows  that  its  limits  coincide 
tolerable  closely  with  area  4  of  Brodmann's  chart  of  the  ana- 


THK    FIIN(;TI0NS    <)1''    TIIK    CKUKUKAI.    COllTKX 


.■^1. 


tomically  dislincl  coiiicul  .-iic'is,  iiiclu(liii<i-,  li«)\v('V(>i-,  :i  pud  of 
the  cortex  farthpi*  foiward  in  area  6. 

The  striicture  of  the  coi-tex  in   the  |)r(M'(Mit  i;il    nioloi-  aica 
(Brodnianii's  area  4  )i8  very  characteristic.     In  this  region  the 


Anus  and  vacina 
Anki";"  I         Sulcus  ..n.rali. 


Shoulder 
Elbow 


\ 

Sulcus  centralis 
"l 
Vocal  cords  Mastication 

Fig.  135. — Brain  of  a  chimpanzee  seen  from  the  left  side  and  from  above, 
upon  which  the  cortical  centers  whose  excitation  causes  bodily  movements 
are  indicated  by  shading.  The  regions  shaded  by  vertical  lines  and  marked 
"eyes"  indicate  the  frontal  and  part  of  the  occipital  regions  which  when 
electrically  excited  cause  conjugate  movements  of  the  eyes.  The  regions 
shaded  with  stipple  comprise  the  motor  projection  centers  from  which  the 
fibers  of  the  pyramidal  tract  arise.  The  names  printed  large  on  the  stippled 
surface  indicate  the  main  regions  of  the  motor  area;  the  names  printed  small 
outside  the  brain  indicate  broadly  bj^  their  pointing  lines  the  relative  topog- 
raphy of  some  of  the  chief  subdivisions  of  the  main  regions  of  the  motor 
cortex.  But  there  exists  much  overlapping  of  the  motor  centers  and  of  their 
subdivisions  which  the  diagram  does  not  attempt  to  indicate.  (After  Griin- 
'bauni  and  Sherrington.) 

fifth  layer  of  the  cortex  (Figs.  127,  133)  contains  a  type  of  large 
pyramidal  cells  (giant  pyramids  or  Betz  cells)  which  are  found 
nowhere  else  in  the  Ijrain.  From  these  cells  tirise  most  of  the 
fibers  of  the  pyramidal  tract  (tractus  cortico-spinalis).  This 
connection  has  been  proved  in  several  ways  in  addition  to  the 


316 


INTRODUCTION    TO   NEUROLOGY 


direct  physiological  experiments  by  electric  stimulation  already 
referred  to.  First,  if  this  area  of  the  cortex  (and  a  portion  of 
area  6  in  front  of  it)  is  destroyed,  the  entire  pyramidal  tract 
will  degenerate,  a  result  which  follows  from  the  destruction  of 
no  other  part  of  the  cortex.  Conversely,  if  the  pyramidal 
tract  is  interrupted,  the  giant  pyramidal  cells  of  this  area  are 
the  only  neurons  of  the  cortex  to  give  clear  pictures  of  chroma- 
tolysis  of  their  chromophilic  substance.  In  the  third  place, 
these  giant  cells  of  the  human  cortex  have  been  counted,  and 


Fig.  136. — The  human  cerebral  hemisphere  seen  from  the  left  side,  upon 
which  the  functional  centers  of  the  cortex  are  indicated.  The  center  marked 
"motor  speech"  is  Broca's  convolution.      (From  Starr's  Nervous  Diseases.) 

a  count  of  the  number  of  fibers  in  the  pyramidal  tract  shows 
that  the  numbers  are  in  tolerably  close  agreement  (nearly 
80,000  on  each  side  of  the  body).  Finally,  a  case  of  sclerotic 
degeneration  involving  almost  the  entire  cortex  has  been 
described  by  Spielmeyer,  in  which  these  giant  cells  and  the 
fibers  of  the  pyramidal  tract  alone  escaped  injury. 

Graham  Brown  and  Sherrington  in  1913  published  some 
important  observations  on  the  functions  of  the  motor  cortex 
of  the  chimpanzee.  After  destruction  of  the  motor  cortex  of 
the  arm  center  in  the  left  precentral  gyrus  there  was  temporary 


THE    FUNCTIONS    OF    THE    CF;REBRAL    CORTEX  317 

loss  of  voluntary  movement  of  the  rifrht  arm,  which  was, 
however,  soon  restored  and  normal  or  nearly  normal  control 
of  arm  movements  was  finally  regained.  Some  months  later 
the  arm  center  of  the  right  precentral  gyrus  was  destroyed. 
This  was  followed  by  temporary  loss  of  voluntary  movement 
of  the  left  arm,  with  gradual  return  to  nearly  normal  control. 
Subsequent  destruction  of  the  area  of  the  right  postcentral 
gyrus  opposite  the  motor  center  of  the  arm  resulted  in  some 
weakness  and  incoordination  of  movements  of  the  left  arm, 
which  gradually  improved.  From  their  experiments  they 
conclude  that  recovery  of  the  use  of  an  arm  may  take  place 
fairly  rapidly  after  the  destruction  of  a  large  part — if  not  the 
whole — of  the  corresponding  area  of  the  motor  cortex.  This 
recovery  is  not  due  to  regeneration  of  the  area  destroj^ed.  It 
is  not  due  to  the  taking  over  by  the  corresponding  area  of  the 
opposite  cerebral  hemisphere  of  the  movements  of  both  arms. 
It  is  not  due  to  the  taking  over  by  the  postcentral  cortex  of 
functions  of  the  motor  cortex.  The  physiological  processes 
involved  in  this  recovery  of  cortical  functions  are  as  yet 
unknown  (see  fuller  report  by  Leyton  and  Sherrington,  19'17). 

The  pyramidal  tract  is  one  of  the  most  important  and  l)est  known  con- 
duction paths  in  the  brain.  This  term  is  often  apphed  to  all  motor 
projection  fibers  arising  in  the  precentral  motor  centers;  but  recent  usage 
inclines  to  limit  its  application  to  the  spinal  fibers  only  of  this  system 
ftractus  cortico-spinalis),  using  the  term  tractus  cortico-bulbaris  for  the 
fibere  of  this  system  Avhich  effect  connection  with  the  motor  cranial  nerves. 

The  complete  destruction  of  the  pyramidal  tract  of  one  side,  or  of  the 
motor  cortex  from  which  its  fibers  arise,  causes  partial  hemiplegia,  i.  e., 
loss  of  voluntary  movement  in  the  trunk  and  limbs  of  one  side.  If  the 
associated  cortico-bulbar  fibers  are  likewise  affected,  the  paralysis  will 
affect  the  muscles  of  the  head  also  on  the  same  side  as  the  limbs  (.total 
liemiplegia).  If  only  a  part  of  the  fibers  of  the  pyramidal  tract  are 
affected,  a  monoplegia  will  result,  i.  e.,  loss  of  movement  in  only  one  limb 
or  group  of  muscles. 

These  projection  fibers  and  their  cell  bodies  in  the  precentral  cortex  are 
known  as  the  "upper  motor  neurons"  and  the  clinical  symptoms  of 
motor  defect  resulting  from  their  injury  are  in  many  respects  different 
from  those  following  destruction  of  the  "lower  motor  neurons,"  i.  e., 
the  peripheral  neurons  whose  cell  bodies  lie  in  the  ventral  gray  cohunns  of 
the  spinal  cord.  In  the  latter  case  the  affected  muscles  will  be  flaccid 
and  will  rapidly  waste  awa>'.  Their  reflexes  will  be  abolished  and  sucli 
patients  show  a  complex  of  symptoms  known  as  the  reaction  of  degenera- 
tion. In  upper  motor  neuron  lesions  the  muscles  retain  their  tone,  which 
may  be  exaggerated;  they  do  not  waste  away;  and  some  of  the  reflexes 
will  persist  in  a  very  characteristic  form. 


318  INTRODUCTION  TO  NEUROLOGY 

By  these  and  other  diagnostic  signs  it  is  usually  possible  for  the  neurolo- 
gist to  determine  with  considerable  accuracy  the  site  of  an  injury  which 
destroys  or  impairs  the  voluntary  motor  path. 

The  exact  mode  of  ending  of  the  fibers  of  the  pyramidal  tract  on  their 
lower  motor  neurons  has  not  been  determined,  and  the  relations  here  are 
very  complex.  It  is  probable  that  in  most,  if  not  in  all  cases  a  short 
neuron  is  intercalated  between  the  upper  and  lower  motor  neurons  in  the 
spinal  cord. 

The  sensory  projection  centers  of  the  cortex  have  also  been 
determined  physiologically,  though  their  limits  are  less  pre- 
cisely known  than  are  those  of  the  motor  cortex.  The  olfac- 
tory receptive  center  has  already  been  mentioned  as  comprised 
within  the  archipallium  (hippocampus  and  hippocampal 
gyrus,  see  p.  241),  only  a  part  of  which  is  exposed  on  the  surface 
of  the  brain  (the  regio  hippocampica  of  Fig.  129;  areas  27, 
28,  34,  35  of  Fig.  131).  The  visual  projection  center,  which 
receives  fibers  from  the  thalamic  optic  centers  in  the  pulvinar 
and  lateral  geniculate  body  (pp.  180,  236),  is  in  the  occipital 
region  (Fig.  129).  Area  17  (Fig.  131)  appears  to  be  the  chief 
center  for  the  reception  of  these  visual  projection  fibers, 
though  the  adjacent  area  18  participates  in  this  function, 
these  areas  together  comprising  the  area  striata  of  the  cortex 
(p.  298).  The  auditory  projection  center  is  in  the  upper  part 
of  the  temporal  lobe  (area  41,  and  probably  to  some  extent 
area  42  also,  of  Fig.  130).  The  tactual  projection  center  lies 
in  the  postcentral  region  (Fig.  128;  areas  1,  2,  and  3  of  Fig. 
130).  The  parts  of  the  cerebral  cortex  which  lie  between  the 
sensory  and  motor  projection  centers  which  have  just  been 
enumerated  are  the  association  centers  (see  pp.  321,  324). 

Within  each  general  sensory  sphere  there  is  a  focal  center 
which  is  exclusively  receptive  in  function,  such  as  area  17 
(Fig.  131)  in  the  visual  sphere.  Each  of  these  focal  centers 
is  surrounded  by  others  which  receive  projection  fibers,  though 
in  less  abundance,  and  also  numerous  association  fibers  from 
other  parts  of  the  cortex.  These  marginal  fields  are,  therefore, 
to  be  regarded  as  association  centers,  each  of  which  is  under  the 
dominant  physiological  influence  of  the  adjacent  focal  pro- 
jection center.  These  are  sometimes  called  visual  psychic, 
auditory  psychic  fields,  etc.,  after  the  adjacent  projection 
centers;  but  these  terms  are  objectionable  as  implying  the  old 


THE    FUNCTIONS    OF    THE    CEREBRAL    CORTEX  310 

phrenological   notion  of  localization  of  specific  psychological 
faculties. 

Each  sensory  projection  center  which  receives  afferent  jBbers 
of  course  sends  out  association  fibers  to  other  parts  of  the  cor- 
tex. Some  of  these  fibers  may  be  very  short,  reaching  only  to 
the  adjacent  marginal  fields  (these  are  arcuate  fibers,  see  Fig. 
121,  f.p.);  other  much  longer  association  fibers  may  assist  in 
forming  the  great  associational  tracts  of  the  subcortical  white 
matter.  The  association  centers  themselves  are  likewise  con- 
nected by  fiber  tracts  of  bewildering  complexitj^,  so  that  every 
part  of  the  cerebral  cortex  is  in  direct  or  indirect  phj^siological 
connection  with  every  other  part.  All  of  these  parts  are, 
therefore,  able  to  influence  the  motor  centers  of  the  precentral 
gyrus,  from  which  alone  voluntary  motor  impulses  can  be  dis- 
charged from  the  cortex  to  the  lower  motor  centers  of  the  brain 
stem  and  spinal  cord. 

The  relations  of  the  tactual  and  souiesthetic  sensory  projection  fibers  to 
the  postcentral  and  precentral  gyri  have  been  variously  described,  and 
some  further  consideration  of  the  functional  connections  of  these  fibers 
may  here  be  appropriate.  From  a  large  body  of  anatomical,  experimen- 
tal, and  clinical  evidence  it  was  formerlj^  assumed  that  the  cortical  motor 
centers  are  coextensive  with  those  for  the  general  somatic  sensory  projec- 
tion S3'stems  of  cutaneous  and  muscular  sensibility,  the  projection  centers 
of  both  the  sensor}-  and  motor  fibers  related  to  each  region  of  the  body 
being  located  on  both  the  anterior  and  posterior  sides  of  the  central  sulcus 
or  fissure  of  Rolando,  that  is,  in  both  the  precentral  and  postcentral  gj'ri. 
-Most  of  the  diagrams  of  cortical  localization  in  all  but  the  most  recent 
manuals  are  based  upon  this  view  of  the  case.  But  recent  work  has 
shown  definitely  that  the  motor  centers  are  confined  to  the  region  in  front 
of  this  sulcus.  Here  only  are  found  the  giant  pj'ramidal  cells  of  Betz 
which  give  rise  to  most  of  the  fibers  of  the  pj'ramidal  tract.  It  may, 
therefore,  be  regarded  as  definiteh^  established  that  motor  projection 
fibers  do  not  arise  from  the  postcentral  gyrus,  as  formerly  supposed. 

Sensory  projection  fibers,  however,  are  known  to  pass  from  the  general 
somatic  sensorj-  centers  in  the  ventral  and  lateral  nuclei  of  the  thalamus 
to  the  postcentral  gyrus,  to  the  motor  cortical  centers  of  the  precentral 
gyrus,  and  to  other  widely  separated  parts  of  the  cortex.  The  significance 
of  this  fa^'t  is  still  obscure.  That  the  postcentral  gyrus  is  of  different 
functional  type  from  the  precentral  gyrus  is  shown  iiy  the  fact  that  motor 
projection  fibers  arise  from  the  latter  and  not  from  the  former,  by  the 
differences  in  anatomical  structure  of  these  regions,  by  a  large  amount  of 
experimental  and  clinical  evidence  which  shows  that  tactile  sensibility  is 
not  lost  by  the  destruction  of  the  precentral  motor  areas,  and  finally  by 
direct  physiological  experiment  upon  human  subjects. 

Dr.  Harvey  Gushing  (1909),  in  opeiating  upon  brain  tumors  in  2  cases 
in  which  the  use  of  an  anesthetic  was  prohibited  by  the  t'ondition  of  the 
patient,  exposed  the  postcentral  gyrus  and,  with  the  patient's  consent, 


320  INTRODUCTION  TO  NEUROLOGY 

electrically  stimulated  its  surface.  The  laatients,  who  were  fully  con- 
scious during  the  operation,  reported  distinct  cutaneous  sensations  which 
were  subjectively  localized  as  if  coming  from  the  skin  of  the  hand.  There 
were  no  motor  responses  from  this  and  adjacent  parts  of  the  cortex  behind 
the  central  sulcus,  though  in  the  same  cases,  upon  stimulation  of  the  pre- 
central  gyrus,  motor  responses  were  obtained  which  were  accompanied 
by  no  sensations  save  those  which  came  from  the  muscles  during  their 
contraction.  In  a  previous  similar  case  Dr.  Gushing  (1908)  obtained 
typical  motor  responses  from  stimulation  (with  the  patient's  consent)  of 
the  precentral  gyrus  in  an  operation  without  anesthesia,  and  these  re- 
siDonses  were  unaccompanied  by  painful  sensations. 

A  very  extensive  series  of  experiments  involving  the  stimulation  and 
extirpation  of  these  cortical  areas  in  apes,  dogs,  and  other  animals  sup- 
ports the  conclusion  that  the  postcentral  gyrus  is  the  great  receptive 
center  for  cutaneous  reactions  of  the  general  cutaneous  system.  What 
may  be  the  functions  of  those  thalamic  fibers  which  pass  to  the  motor 
centers  in  front  of  the  central  fissure  is  unsettled.  Possibly  these  con- 
nections are  concerned  in  cortical  reflexes  of  the  proprioceptive  system  or 
acquired  automatisms. 

The  myelinated  fibers  of  the  cerebral  hemisphere  mature, 
that  is,  acquire  their  myelin  sheaths,  at  various  stages  in  the 
development  of  the  brain,  some  of  these  systems  of  fibers  ap- 
pearing before  birth  and  some  after  birth.  Much  investiga- 
tion has  been  directed  to  the  determination  of  the  exact  facts 
regarding  the  sequence  of  development  of  these  fibers,  and 
many  interesting  theories  have  been  developed  regarding  the 
significance  of  these  facts. 

Flechsig  in  a  long  series  of  researches  made  the  first  thorough  study  of 
this  problem,  and  his  conclusions  have  exerted  a  profound  influence  upon 
all  subsequent  theories  of  the  functions  of  the  cerebral  cortex.  He  pro- 
posed a  series  of  laws  of  developmental  sequence  (myelogeny)  of  the  cor- 
tical fibers,  among  which  two  maj^  be  mentioned:  (1)  The  myelinated  fiber 
tracts  of  the  brain  do  not  all  mature  at  the  same  time,  and  fiber  systems 
which  are  of  hke  function,  that  is,  which  are  so  connected  as  to  perform 
special  movements  in  response  to  excitation,  tend  to  mature  at  the  same 
time.  This  is  Flechsig's  "fundamental  myelogenetic  law,"  which  may 
be  stated  in  this  form.  The  myelination  of  the  nerve-fibers  of  the  develop- 
ing brain  follows  a  definite  sequence  such  that  the  fibers  belonging  to  par- 
ticular functional  systems  mature  at  the  same  time.  (2)  A  second  law 
states  that  in  the  cerebral  cortex  there  are  two  great  functional  groups  of 
fibers  which  mature  at  different  times.  One  of  these  groups  contains  the 
projection  fibers,  which  mature  early,  chiefly  before  birth;  the  other  group 
contains  the  association  fibers,  which  mature  after  birth.  These  groups 
are  further  subdivided  into  subsidiary  functional  systems,  each  of  which 
connects  with  a  definite  region  of  the  cerebral  cortex,  so  that  it  is  possible 
to  map  the  cortical  areas  in  accordance  with  the  sequence  of  development 
of  the  related  myelinated  fibers.  There  are,  accordingly,  two  groups  of 
cortical  areas  in  this  scheme:  the  projection  centers  whose  fibers  mature 
early  and  the  association  centers  whose  fibers  mature  late. 


THE  FUNCTIONS  OF  THE  CEREBRAL  CORTEX      ;!21 

Figures  137  and  138  illustrate  the  arrangement  of  these  ai-eas,  the  pri- 
mary areas  (projection  centers)  being  marked  by  double  cross-hatching  and 
the  association  centers  by  single  cross-hatching  or  unshaded  areas.  TIk; 
numbers  printed  on  the  charts  indicate  the  approximate  order  in  which 
the  corresponding  parts  acquire  their  myelinated  fibers.  It  will  be 
noticed  that  FlecTisig's  projection  areas  do  not  correspond  exactly  with 
those  determined  by  the  physiological  method  and  bj^  the  histological 
study  of  the  adult  cortex  (Figs.  130,  131,  135,  136). 

On  the  basis  of  his  studies,  Flechsig  elaborated  a  highly  speculative 
theory  of  the  significance  of  the  association  centers,  which  has  been  criti- 
cized as  a  return  to  the  old  attempt  to  localize  particular  mental  functions 
in  definite  cortical  areas.  These  criticisms  are  not  wholly  justified ;  never- 
theless it  is  even  yet  premature  to  attempt  so  detailed  an  analysis  of  the 
cortical  mechanisms  of  psychic  processes  as  Flechsig  has  elaborated.  His 
observations  on  the  facts  of  myelogeny,  moreover,  have  not  been  con- 
firmed bjr  more  recent  students  of  the  question  (IVIonakoAv,  Vogt,  De- 
jerine,  and  others),  though  it  seems  to  be  established  that  the  sensory  and 
motor  projection  centers  in  general  acquire  myelinated  fibers  earlier  than 
other  parts  of  the  cerebral  cortex.  (This  entire  question  is  criticallj^  re- 
viewed by  Brodmann  inLewandowsky's  Handbuch  der  Neurologic,  Band 
1,  pp.  234-244).  The  only  conclusion  at  present  possible  is  that'  the 
factors  wdiich  operate  in  determining  the  sequence  of  myelination  of  the 
nerve-fibers  of  the  brain  are  exceedingly  complex,  and  it  is  impossible  from 
the  facts  at  present  known  to  formulate  the  laws  of  the  mj^elogenetic 
development  of  the  brain. 

Attention  should  be  called  here  to  the  fact  that  there  are 
many  different  kinds  of  projection  fibers,  that  is,  fibers  con- 
necting the  cerebral  cortex  with  the  underlying  structures  of 
the  brain  stem  and  spinal  cord.  Most  of  these  projection 
fibers,  except  those  of  the  olfactory  system,  pass  thi-ough  the 
corona  radiata  and  internal  capsule  of  the  corpus  striatum. 
The  most  important  of  these  projection  systems  are  the  great 
sensory  radiations  which  discharge  their  nervous  impulses  into 
the  cortical  centers  of  vision,  hearing,  touch,  and  smell,  as 
already  described  (the  exact  course  of  the  gustatory  projection 
fibers  has  not  been  determined),  and  the  great  motor  sj'-stem 
of  the  pyi-amidal  tract  arising  from  the  precentral  gj^rus. 
Each  of  the  thalamo-cortical  projection  tracts  of  vision,  hear- 
ing, and  tactile  sensibility  is,  moreover,  accompanied  by 
corlico-thalamic  fibers  which  conduct  in  the  reverse  direction 
and  whose  functions  are  not  well  known,  and  there  are  other 
cortico-thalamic  and  cortico-mesencephalic  systems.  The 
cerebral  cortex  is  in  direct  connection  with  the  red  nucleus  of 
the  cerebral  peduncle  by  a  cortico-rubral  tract,  arising  in  the 
frontal  region  of  the  cortex,  and  by  ascending  fibers  from  the 

21 


322 


INTRODUCTION    TO    NEUROLOGY 


Fig.  138 
Figs.  137,  138. — Lateral  and  median  views  of  the  human  cerebral  hemi- 
sphere, to  illustrate  the  sequence  of  maturity  of  the  myelinated  fibers  of  the 
cortex  during  the  development  of  the  brain,  according  to  Flechsig's  observa- 
tions. The  numbers  indicate  approximately  the  order  in  which  different 
parts  of  the  cortex  acquire  their  mature  fibers.  Areas  1-12  (double  cross- 
hatched)  constitute  the  primordial  region,  made  up  chiefly  of  the  projection 
centers;  these  include  the  olfactory  area  (1,  3,  4,  and  4a),  the  somesthetic 
area  (2,  2?),  2c,  and  8),  the  visual  area  (5),  and  the  auditory  area  (7  and  prob- 


THE  FUNCTIONS  OF  THE  CEREBRAL  CORTEX      323 

red  nucleus  to  the  same  general  part  of  the  cerebral  hemisphei(\ 
From  the  frontal,  parietal,  temporal,  and  occipital  association 
centers  there  arise  large  descending  fiber  tracts  to  the  nuclei 
of  the  pons  (cortico-pontile  tracts).  These  connections  be- 
tween the  cerebral  cortex  and  the  red  nucleus  and  pons  put  the 
cerebral  cortex  and  the  cerebellum  into  very  intimate  relations, 
but  the  exact  way  in  which  the  cerebrum  and  the  cerebellum 
cooperate  functionally  is  obscure  (see  p.  215). 

From  the  preceding  account  it  is  plain  that  the  cere))ral  cor- 
tex is  structurally  differently  organized  in  different  parts,  and 
that  each  of  these  parts  has  its  own  characteristic  fiber  connec- 
tions. Physiological  experiment  and  pathological  studies  have 
shown,  moreover,  that  sonte  of  these  regions,  the  projection 
centers,  are  functionally  diverse,  in  that  each  one  receives  a 
particular  type  of  afferent  fibers  or  discharges  efferent  impulses 
into  a  definite  subcortical  motor  center.  Stated  in  other 
words,  the  cortex  is  structurally  a  mosaic  of  diverse  patterns; 
and  on  the  physiological  side  there  is  a  specific  localization  of 
function,  at  least  in  the  sense  that  the  various  systems  of 
afferent  and  efferent  projection  fibers  connect  each  with  its 
particular  place  in  the  structural  mosaic. 

Several  English  neurologists,  notably  Bolton,  from  studies  on  the 
development  and  adult  structure  of  the  cortex  in  normal  and  abnormiU 
men  and  in  other  mammals,  have  been  led  to  the  conclusion  that,  in  addi- 
tion to  the  mosaic  localization  pattern  of  which  we  have  been  speaking, 
there  is  a  functional  difference  between  the  different  layers  of  neurons  of 
the  cortex  in  general.  Bolton  beheves  that  the  granular  layer  (layer  IV 
of  Fig.  127)  marks  an  important  boundary  between  functionally  different 
cortical  mechanisms.  The  infragranular  portion  of  the  cortex  is  thought 
to  be  concerned  especially  with  the  performance  of  the  simpler  sensori- 
motor reactions,  particularly  those  of  the  instinctive  type,  while  the 
supragranular  layers  serve  the  higher  associations  manifested  by  the 
capacitv  to  learn  by  individual  experience  and  to  develop  the  intellectual 
life. 

The  infragranular  layers  mature  earlier  in  the  development  of  the  brain, 
and  they  are  the  last  to  suffer  degeneration  in  the  desti'uction  of  cortical 
cells  in  the  acute  dementias  or  insanities.  Tlie  supragranular  layers 
(notably  the  pyramidal  neurons  of  Brodmann's  third  layer,  Fig.  127)  ma- 

ably  76),  aud  the  gustatory  area  {ib  and  6).  The  reiuainder  of  the  corte.x  is 
made  up  of  association  centers,  of  which  there  are  two  groups,  those  which 
mature  soon  after  birth  (hghtly  shaded  areas  13-28),  and  the  terminal  areas 
(unshaded  areas  28-36)  which  are  the  last  to  mature.  (From  Lewandowsky's 
Handbuch  der  Neurologie.) 


324  INTRODUCTION  TO  NEUROLOGY 

ture  later  than  any  other  layers.  They  are  thinner  in  lower  animals  and 
in  feeble-minded  and  imbecile  men  than  in  the  normal  man,  and  they  are 
the  first  to  show  degenerative  changes  in  dementia. 

This  doctrine  is  controverted  by  some  other  neurologists,  but  the  evi- 
dence seems  to  show  that  the  supragranular  pyramidal  neurons  are 
physiologically  the  most  important  elements  in  the  higher  associative  proc- 
esses of  the  cortex.  In  this  connection  it  is  significant  that  the  granular 
and  infragranular  layers  are  thicker  in  the  projection  centers,  while  in  the 
association  centers  the  supragranular  layers  of  pyramidal  cells  are  thicker. 
But  all  of  the  layers  in  each  region  are  very  intimately  related,  the  proc- 
esses of  most  of  the  cells  of  the  deeper  layers  extending  throughout  the 
thickness  of  the  more  superficial  layers  (see  Figs.  123,  124,  125)  to  reach 
the  most  superficial  layer,  and  in  the  present  state  of  our  knowledge  a  func- 
tional difference  between  the  layers  cannot  be  said  to  have  been  estab- 
lished, save  in  very  general  terms. 

It  must  be  borne  in  mind  that  the  most  significant  parts  of 
the  human  cerebral  cortex  are  the  association  centers.  These 
alone  are  greatly  enlarged  in  the  human  brain  as  compared 
with  those  of  the  higher  apes.  In  the  latter  animals  the  pro- 
jection centers  are  fully  as  large  as  those  of  man,  the  much 
smaller  brain  weight  being  chiefly  due  to  the  relatively  poor  de- 
velopment of  the  association  centers. 

The  data  which  we  have  summarized  in  the  preceding  pages 
have  led  to  the  most  contradictory  theories  as  to  the  exact 
mode  of  functioning  of  the  association  centers.  Neurologists 
have  been  prone,  even  up  to  the  present  time,  to  fall  into  the 
error  of  attempting  to  find  specific  centers  for  particular  mental 
functions  or  faculties.  But  the  evidence  at  present  available 
gives  small  promise  of  success  in  the  search  for  such  centers 
It  is,  in  fact,  theoretically  improbable  that  such  discoveries 
will  ever  be  made,  for  psychology  today  recognizes  no  such 
mosaic  of  discrete  mental  faculties  as  would  be  implied  in  such 
a  doctrine. 

The  facts  of  cerebral  localization  as  clinically  and  experi- 
mentally demonstrated,  in  themselves  and  aside  from  any 
philosophic  theories  based  upon  them,  contribute  no  evidence 
whatever  to  a  solution  of  the  problem  of  a  seat  of  conscious- 
ness or  of  particular  mental  "faculties."  That  the  proper 
functioning  of  a  given  locus  in  the  cortex  is  essential  to  the 
execution  of  a  given  motion  or  the  experience  of  a  given  sensa- 
tion by  no  means  necessarily  implies  that  the  consciousness  of 
the  act  is  located  there.     The  latter  is  an  entirely  independent 


THK    FUNCTIONS    OF    THE    CKREBKAL    COKTEX  325 

problem  whicli  must  be  separately  investigated,  ll  is  not, 
then,  the  facts  of  cerebral  localization  which  can  be  called  in 
({uestion  so  much  as  the  interpretation  of  these  facts. 

The  search  for  a  single  seat  of  consciousness,  such  as  psy- 
chologists and  philosophers  have  so  long  sought,  is  vain.  The 
higher  mental  processes  undoubtedlj''  reciuire  the  activity  of 
association  centers  of  the  cerebral  cortex,  and  the  integrity  of 
the  associational  mechanism  as  a  whole  is  essential  for  their  full 
efficiency.  The  cerebral  cortex  differs  from  the  reflex  centers 
of  the  brain  stem  chiefly  in  that  all  of  its  parts  are  intercon- 
nected by  inconceivably  complex  S5'"stems  of  associational  con- 
nections, many  of  which  are  probably  acquired  late  in  life 
under  the  influence  of  individual  experience,  and  any  combina- 
tion of  which  may,  under  appropriate  conditions  of  external 
excitation  and  internal  physiological  state,  become  involved  in 
any  cerebral  process  whatever. 

Nevertheless,  some  of  these  cortical  association  paths  are 
structurallj^  more  highly  elaborated  than  others  (Fig.  121,  p. 
296,  illustrates  the  most  distinct  of  these  tracts),  and  certain 
combinations  of  cortical  functions  are,  therefore,  more  likely  to 
follow  a  given  stimulus  than  others.  This  associational  pat- 
tern is  doubtless  partly  innate  and  partly  acquired.  That 
there  is  a  fau'ly  precise  anatomical  pattern  of  association  tracts 
can  be  seen  in  anj^  good  dissection  of  the  cerebral  hemisphere, 
and  that  the  elements  of  this  pattern  are  related  in  definite 
functional  systems  which  are  spatially  separate  is  shown  by 
numberless  clinical  observations  in  which  sharply  circum- 
scribed mental  defects  are  found  to  "be  associated  with  definite 
cerebral  lesions.  The  phenomena  of  aphasia  give  the  clearest 
illustrations  of  these  relations. 

The  term  aphasia  has  commonly  been  applied  to  a  variety  of 
speech  defects,  but  Hughlings  Jackson  extended  the  connota- 
tion of  the  word  to  include  "a  loss  or  defect  in  symbolizing  re- 
lations of  things  in  any  way."  The  lesion  which  produces  the 
defect  affects  the  association  centers  rather  than  the  projection 
centers,  for  there  is  no  primary  sensory  defect — no  blindness  or 
deafness  or  loss  of  general  sensation — nor  is  there  any  motor 
paralysis. 

The  problems  connected  with  aphasia  are  very  difficult  and 


328  INTRODUCTION  TO  NEUROLOGY 

confused,  and  there  is  by  no  means  general  agreement  on  either 
the  fundamental  physiological  mechanisms  involved  in  speech 
or  on  the  nature  of  the  lesions  which  produce  the  various  types 
of  observed  speech  defects.  The  enormous  literature  relating 
to  this  subject  cannot  be  summarized  here;  see  the  text-books 
of  physiology,  physiological  psychology,  and  clinical  neurology. 

Lesions  of  the  primary  sensory  or  motor  projection  centers  will  not  pro- 
duce aphasia,  for  in  these  cases  all  sensations  or  all  movements  related  to 
the  injured  parts  are  lost,  whereas  in  aphasia  only  the  correlations  in- 
volved in  speech  or  other  associational  processes  are  impaired  and  all  other 
sensorimotor  correlations  may  be  intact.  Of  course,  the  number  of  asso- 
ciational pathways  involved  in  the  communicating  of  ideas  by  hearing, 
reading,  speaking,  and  writing  words  is  very  large;  and  the  character  ot 
the  speech  defect  will  depend  in  part  upon  the  particular  associational 
tracts  affected  by  the  lesion  and  in  part  upon  the  effect  of  the  lesion  upon 
the  general  intelligence  of  the  patient  (diaschisis  effect,  see  p.  327).  The 
second  factor  seems  to  be  exceedingly  variable  and  has  given  rise  to  much 
controversy. 

Distinctive  names  have  been  given  to  the  more  important  types  of 
speech  defect  as  clinically  observed;  such  as  agraphia  or  inabihty  to  write 
correctly,  aphemia  or  inability  to  utter  words,  word-blindness  (alexia}  or 
inability  to  comprehend  written  words,  word-deafness  or  inability  to 
comprehend  spoken  words,  and  many  others.  Evidently  an  aphasia  may 
result  from  injury  to  (1)  a  sensory  association  area  contiguous  to  the  pri- 
mary visual  or  auditory  projection  centers  (sensory  types  of  aphasia),  or 
(2)  to  a  motor  association  center  contiguous  to  the  motor  projection 
centers  for  the  speech  muscles  (motor  types),  or  (-3)  to  any  of  the  associa- 
tional tracts  connecting  these  association  centers. 

The  second,  or  motor,  type  of  aphasia  usually,  though  not  invariably, 
results  from  injury  to  the  posterior  part  of  the  inferior  frontal  gyrus  (see 
Fig.  54,  p.  130)  of  the  left  hemisphere  in  right-handed  persons  and  of  the 
right  hemisphere  in  left-handed  persons.  This  relation  was  first  discov- 
ered by  Broca,  and  the  area  of  motor  speech  correlations  (marked  "motor 
speech"  in  Fig.  136,  p.  316)  has  since  been  termed  Broca's  convolution. 

It  should  be  reiterated  that  Broca's  convolution  does  not  lie  in  the  excit- 
able motor  zone  of  the  cortex.  Though  the  destruction  of  this  area  may 
be  followed  by  defects  of  speech,  the  muscles  of  the  larynx,  tongue,  lips, 
etc.,  involved  in  vocalization  are  not  paralyzed.  This  case  is  typical  of 
many  other  motor  association  centers  of  the  cortex  whose  integrity  is 
essential  for  specific  motor  combinations,  though  separate  motor  centers 
are  present  for  all  of  the  muscles  involved  in  these  movements. 

The  correlations  involved  in  the  motor  functions  of  speech  appear  to  be 
represented  typically  in  only  one  hemisphere,  though  this  is  by  no  means 
rigidly  true.  The  corresponding  structures  in  the  other  hemisphere  may- 
cooperate  in  these  functions  normally,  and  after  loss  of  speech  from  a  uni- 
lateral lesion  speech  may  be  reacquired  by  further  education  of  the  unin- 
jured centers  of  the  same  or  the  opposite  side.  It  has  recently  been  shown 
that  Broca's  convolution  is  often  larger  on  the  left  side  of  the  brain  than 
on  the  right  side  and  that  the  average  thickness  of  the  cortex  in  this  region 
is  greater  on  the  left  side. 


THP:  FUNCTION'S  OF  THE  CEREBRAL  CORTEX      327 

Various  attempts  Ixave  been  made  to  localize  each  of  the  various  types 
of  aphasia  mentioned  above  in  a  specific  part  of  the  cortex,  but  witli  no 
concordant  results.  Each  of  these  functions  is,  of  course,  very  complex, 
and  a  small  circumscribed  cortical  injury  may  disturb  or  temporarily 
abolish  the  entire  complex  by  the  destruction  of  one  only  of  the  compo- 
nent functional  connections.     (See  the  summary  by  Dr.  A.  Meyer,  1910.) 

The  general  conclusion  to  be  drawn  from  the  entire  series  of 
physiological  and  pathological  studies  of  the  cortex  is  that  spe- 
cific mental  entities  are  not  resident  in  particular  cortical  areas, 
but  that  cortical  functions  involve  the  discharge  of  nervous  en- 
ergy from  one  or  more  sensory  centers  to  various  near  and  re- 
mote regions,  each  of  which,  in  turn,  may  serve  as  a  point  of 
departure  for  new  nervous  discharges,  and  so  on  until  the  com- 
plexity of  action  and  interaction  of  part  upon  part  becomes  too 
intricate  for  the  mind  to  conceive.  The  resultant  effect  of  all 
of  these  nervous  activities  which  reverberate  from  one  associa- 
tion center  to  another  will  be  the  establishment  of  some  sort  of 
a  neural  equilibrium  which  finds  its  expression  in  a  definite 
motor  act  or  an  idea.  The  nature  of  this  physiological  process 
is  still  unknown. 

This  dynamic  view  of  cortical  function  finds  a  further  illus- 
tration in  the  realm  of  neuro-pathology  in  von  Monakow's  doc- 
trine of  diaschisis.  The  onset  of  cerebral  hemorrhage  or  any 
other  sudden  injury  to  the  cerebral  cortex  is  usually  marked  by 
an  apoplectic  ''stroke,"  with  profound  shock  and  usually  loss 
of  consciousness.  The  entire  cortical  equilibrium  is  dis- 
turbed and  this  effect  irradiates  very  widely  throughout  the 
nervous  system.  If  the  injury  is  not  too  severe,  there  is  soon 
a  partial  readjustment  of  the  nervous  equilibrium  and  con- 
sciousness returns.  But  the  restoration  is  incomplete,  for 
some  of  the  normal  factors  in  the  dynamic  equilibrium  complex 
are  lacking  by  reason  of  the  destruction  of  the  corresponding 
cortical  areas  or  association  tracts.  The  intelligence  is  en- 
feebled and  all  voluntary  control  is  impaired.  In  the  course  of 
a  few  weeks  or  months  a  new  equilibrium  minus  the  lacking 
factors  is  established  and  the  patient  vei-y  rapidly  improves. 
Ultimately  complete  recovery  may  occur,  save  for  a  permanent 
residual  defect  which  i-esults  directly  from  the  loss  of  the  tissue 
destroyed. 

The  immediate  shocik-like  hiterference  with  the  activitv  of 


328  INTRODUCTIOlSr    TO    NEUROLOGY 

cerebral  centers  not  directly  affected  by  the  lesion  is  what  von 
Monakow  means  by  diaschisis.  Upon  the  restoration  of  the 
nervous  equilibrium  this  transient  diaschisis  effect  is  wholly  or 
partially  lost,  and  the  residual  symptoms  of  defect  give  a  fairly 
accurate  picture  of  the  intrinsic  functions  of  the  center  directly 
attacked  by  the  lesion.  It  is  commonly  assumed  that  there 
is  also  during  the  process  of  gradual  recovery  from  such  a  corti- 
cal injury  a  certain  capacity  for  the  compensatory  develop- 
ment of  other  centers  of  the  same  or  the  opposite  cerebral  hemi- 
sphere, so  that  they  learn  to  perform  vicariously  the  functions 
of  the  lost  part. 

All  functions  of  the  nervous  system  are  facilitated  by  repeti- 
tion, and  many  such  repetitions  lead  to  an  enduring  change  in 
the  mode  of  response  to  stimulation  which  may  be  called  physio- 
logical habit.  This  implies  that  the  performance  of  every 
reaction  leaves  some  sort  of  a  residual  change  in  the  structure  of 
the  neuron  systems  involved.  These  acquired  modifications 
of  behavior  are  manifested  in  some  degree  by  all  organisms 
(see  pp.  22,  33),  and  this  capacity  lies  at  the  basis  of  all  asso- 
ciative memory  (whether  consciously  or  unconsciously  per- 
formed) and  the  capacity  of  learning  by  experience.  This 
modifiability  through  individual  experience  is  possessed  by  the 
cerebral  cortex  in  higher  degree  than  by  any  other  part  of  the 
nervous  system;  and  the  capacity  for  reacting  to  stimuli  in 
terms  of  past  experience  as  well  as  of  the  present  situation  lies 
at  the  basis,  of  that  docility  and  intelligent  adaptation  of  means 
to  ends  which  are  characteristic  of  the  higher  mammals.  It  is 
a  fact  of  common  observation  that  those  animals  which  possess 
the  capacity  for  intelligent  adjustments  of  this  sort  have 
larger  association  centers  in  the  cerebral  cortex  than  do  othe?- 
species  whose  behavior  is  controlled  by  more  simple  reflex 
and  instinctive  factors,  that  is,  by  inherited  as  contrasted  with 
individually  acquired  organization.  This  is  brought  out  with 
especial  distinctness  by  a  comparison  of  the  brains  of  the  higher 
apes  with  that  of  man  (Figs.  132,  133),  and  of  the  lower  races 
of  men  as  contrasted  with  the  higher.  In  our  own  mental 
life  we  recognize  the  persistence  of  traces  of  previous  experi- 
ence subjectively  as  memory,  and  memory  lies  at  the  basis  of 
all  human  culture.  -  From  this  it  follows  that  psychological 


THE  FUNCTIONS  OF  THE  CEREBRAL  CORTEX      329 

memory  is  probably  a  function  of  the  association  centers;  but 
it  must  not  be  assumed  that  specific  memories  reside  in  par- 
ticular cortical  areas,  much  less  that  they  are  preserved  as 
structural  traces  left  in  individual  cortical  cells,  as  has  some- 
times been  done.^ 

The  simplest  concrete  memory  that  can  appear  in  conscious- 
ness is  a  very  complex  process,  and  probably  involves  the  ac- 
tivity of  an  extensive  system  of  association  centers  and  tracts. 
That  which  persists  in  the  cerebral  cortex  between  the  initial 
experience  and  the  recollection  of  it  is,  therefore,  in  all  proba- 
bility a  change  in  the  interneuronic  resistance  such  as  to  alter 
the  physiological  equilibrium  of  the  component  neurons  of 
some  particular  associational  system.  What  the  nature  of 
this  change  may  be  is  unknown,  but  it  is  conceivable  that  it 
might  take  the  form  of  a  permanent  modification  of  the  syn- 
apses between  the  neurons  which  were  functionally  active 
during  the  initial  experience  such  as  to  facilitate  the  active 
participation  of  the  same  neurons  in  the  same  physiological 
pattern  during  the  reproduction. 

That  which  we  know  subjectively  as  the  association  of  ideas 
may,  in  a  somewhat  similar  way,  be  pictured  as  involving 
neurologic  ally  the  discharge  of  nervous  energy  in  the  cortex 
between  two  systems  of  neurons  which  have  in  some  previous 
experience  been  physiologically  united  in  some  cortical  reac- 
tion. If,  for  instance,  I  heard  a  song  of  a  mocking  bird  for 
the  first  time  last  year  while  walldng  in  a  rose  garden,  upon 
revisiting  the  garden  I  may  recall  the  song  of  the  bird.  Here 
the  sight  of  the  garden  (a  highly  complex  apperceptive  process 
invohdng  many  association  tracts)  actuates  neuron  sj^stem 
number  one  dominated  by  present  visual  afferent  impulses,  and 
the  association  tract  leading  to  neuron  system  number  two 
(the  auditory  complex  established  last  year  when  the  song  was 
heard)  has  a  lowered  physiological  resistance  by  virtue  of  the 
previous  collocation  with  system  number  one,  and  I  remember 
the  song  (see  p.  67). 

•  These  residua  of  past  cerebral  activities  form  the  oasis  of  those  char- 
acteristic "brain  dispositions"  which  are  important  factors  in  each  per- 
sonalitj'.  They  have  been  termed  "engrams"  by  Semon  and  "neuro- 
grams''  bv  Morton  Prince  (see  Prince,  the  Unconscious,  Chapter  V, 
New  York,  1914). 


330  INTKODUCTION  TO  NEUROLOGY 

It  should  be  emphasized  that  the  mechanism  of  association 
here  suggested  is  purely  theoretical;  we  have  no  scientific  evi- 
dence regarding  the  details  of  such  physiological  processes. 
But  it  can  be  confidently  asserted  that  even  the  simplest  asso- 
ciational  processes  are  at  least  as  complex  as  this,  and  may 
involve  the  participation  of  thousands  of  neurons  in  widely 
separate  parts  of  the  cortex;  and  the  consciousness  must  be 
regarded  as  a  function  of  the  entire  process,  not  of  any  de- 
tached center  (cf.  p.  69). 

In  summarizing  this  dynamic  conception  of  the  nature  of  consciousness 
I  will  quote  a  few  sentences  from  my  brother's  writings  (see  C.  L.  Herrick, 
1910,  pp.  13,  14): 

"The  theory  of  consciousness  which  seems  best  to  conform  to  the  condi- 
tions of  brain  structure  and  its  observed  unity  is  that  each  conscious  state 
is  an  expression  of  the  total  equilibrium  of  the  conscious  mechanism,  and 
that  intercurrent  stimuli  are  continually  shifting  the  equilibrium  from  one 
to  another  class  of  activities.  In  other  words,  the  sensation  accompany- 
ing a  given  color  presentation  is  not  due  to  the  vibrations  in  the  visual 
center  in  the  occipital  lobe,  but  to  the  state  of  cortical  equilibrium  or  the 
equation  of  cortical  excitement  when  that  color  stimulus  predominates. 
Previous  vestigial  excitements  and  coordinations  [associations,  c.  J.  h., 
see  p.  37]  with  the  data  from  other  cortical  centers  all  enter  into  the  con- 
scious presentation.  As  the  wave  of  excitation  passes  from  the  visual 
center  to  other  parts,  the  proportional  participation  of  other  centers 
increases,  producing  a  composite  containing  more  distantly  related 
elements." 

"Every  specific  sense-content  with  its  escort  of  reflexly  produced  asso- 
ciated elements  causes  a  more  or  less_  profound  disturbance  of  the  psy- 
chical equilibrium,  and  the  nature  of  this  disturbance  depends  not  only  on 
the  intensity  and  state  of  concentration,  but  very  largely  on  the  kind  of 
equilibrium,  already  existing.  .  .  .  The  character  of  the  conscious  act 
(and  the  elements  of  consciousness  are  always  acts)  will,  of  course,  depend 
upon  the  extent  to  which  the  several  factors  in  the  associational  system 
participate  in  the  equilibrium.  Each  disturbance  of  the  equilibrium 
spreads  from  the  point  of  impact  in  such  a  way  that  progressively  more 
of  the  possible  reflex  currents  enter  the  complex,  thus  producing  the  ex- 
tension from  mere  sensation  to  the  higher  processes  of  apperceptive 
association.  A  conscious  act  is  always  a  fluctuation  of  equilibrium,  so 
that  all  cognitive  elements  are  awakened  in  response  to  changes  rather 
than  invariable  or  monotonous  stimuli." 

The  dynamic  view  of  consciousness  here  adopted  makes  such 
expressions  as  "the  unconscious  mind"  impossible  contradic- 
tions. Either  the  mental  functions  are  in  process  or  they  are 
not,  and  unconscious  cerebration  is  not  consciousness.  This 
is,  of  course,  not  incompatible  with  a  dissociation  of  conscious- 
ness into  multiple  or  co-conscious  units,  as  Dr.  Morton  Prince 


THE    FUNCTIONS    OF    'I'HE    CP^REBRAL    CORTEX  331 

SO  forcibly  illustrates  (The  Unconscious,  p.  249),  though  how 
far  in  normal  men  this  dissociation  may  be  carried  is  an  open 
question. 

In  my  life  as  viewed  by  an  outside  observer  there  is  continu- 
ity of  process,  but  not  necessarily  continuity  of  consciousness. 
In  my  own  experience  consciousness  appears  to  be  continuous, 
of  course,  because  the  periods  of  unconsciousness  (as  in  coma, 
deep  sleep,  etc.)  do  not  appear  in  consciousness;  that  is,  they 
do  not  exist  for  me  except  as  I  learn  of  them  by  an  indirection. 
In  a  water  mill  the  function  of  grinding  corn  may  go  on  inter- 
mittently, though  the  mechanism  is  there  all  the  time  and  the 
energy  is  there;  but  if  the  water  passes  from  the  mill  race  out 
over  the  dam  instead  of  through  the  water  wheel  the  grinding 
function  ceases.  While  the  mill  is  at  rest  changes  may  be  made 
in  the  machinerj^  which  will  modify  the  character  of  the  grind- 
ing when  it  is  resumed,  but  these  changes  are  not  grinding. 
So  in  the  brain  the  mechanism  of  consciousness  and  the 
structural  memory  vestiges  of  past  experience  may  be  present 
continuously;  indeed,  these  vestigeal  traces  may  be  linked  up 
in  new  ways  by  intercurrent  physiological  processes.  But 
these  things  do  not  constitute  consciousness.  In  fact,  a 
large  amount  of  unconscious  cerebration  may  go  on,  the  end 
result  of  which  alone  becomes  conscious.  The  aim  of  physio- 
logical psychology  is  to  clarify  not  only  the  mechanism  of 
consciousness,  but  also  all  of  the  antecedent  and  subsequent 
physiological  processes  which  are,  from  the  standpoint  of  an 
outside  observer,  demonstrably  related  to  the  conscious 
processes.  It  is  possible,  moreover,  to  develop  a  really 
scientific  introspective  psychology  in  whick  abstraction  is  made 
from  all  of  these  mechanisms  and  the  individual  experiences 
alone  are  studied  as  given  in  consciousness.  This  makes  up  a 
large  part  of  general  psychology. 

Summary. — The  functions  of  the  cerebral  cortex  are  still 
largely  wrapped  in  mystery,  but  the  evidence  thus  far  accumu- 
lated suggests  that  these  functions  are,  so  far  as  physiologically 
known,  not  different  in  kind  from  those  of  the  other  parts  of  the 
brain.  It  is,  however,  manifest  that  these  functions  are  con- 
cerned with  the  individually  acquired  and  especially  the  intelli- 
gently performed  activities  as  distinguished  from  the  funda- 


332  INTRODUCTION  TO  NEUROLOGY 

mental  reflex  and  instinctive  processes  whose  mechanisms  are 
innate.  There  is  a  specific  locaUzation  of  function  in  the 
cerebral  cortex,  in  the  sense  that  particular  systems  of  sensory 
projection  fibers  terminate  in  special  regions  (the  sensory 
projection  centers),  that  from  other  special  regions  (the  motor 
projection  centers)  particular  systems  of  efferent  fibers  arise 
for  connection  with  the  lower  motor  centers  related  to  groups 
of  muscles  concerned  with  the  bodily  movements,  and  that 
between  these  projection  centers  there  are  association  centers, 
each  of  which  has  fibrous  connections  of  a  more  or  less  definite 
pattern  with  all  other  parts  of  the  cortex.  The  destruction 
of  any  part  of  the  cortex  or  of  the  fiber  tracts  connected  there- 
with involves,  .first,  a  permanent  loss  of  the  particular  func- 
tions served  by  the  neurons  affected,  and,  in  the  second  place, 
a  transitory  disturbance  of  the  cortical  equilibrium  as  a  whole 
(diaschisis  effect).  Specific  mental  acts  or  faculties  are  not 
resident  in  particular  cortical  areas,  but  all  conscious  processes 
probably  require  the  discharge  of  nervous  energy  throughout 
extensive  regions  of  the  cortex,  and  the  character  of  the  con- 
sciousness will  depend  in  each  case  upon  the  dynamic  pattern 
of  this  discharge  and  the  sequence  of  function  of  its  component 
systems.  This  pattern  is  inconceivably  complex  and  only 
the  grosser  features  are  at  present  open  to  observation  by 
experiment  and  pathological  studies. 

No  cortical  area  can  properly  be  described  as  the  exclusive 
center  of  a  particular  function.  Such  "centers"  are  merely 
nodal  points  in  an  exceedingly  complex  system  of  neurons 
which  must  act  as  a  whole  in  order  to  perform  any  function 
whatsoever.  Their  relation  to  cerebral  functions  is  analogous 
to  that  of  the  railway  stations  of  a  big  city  to  traffic,  each 
drawing  from  the  whole  city  its  appropriate  share  of  passengers 
and  freight;  and  their  great  clinical  value  grows  out  of  just 
this  segregation  of  fibers  of  like  functional  systems  in  a  narrow 
space,  and  not  to  any  mysterious  power  of  generating  psychic 
or  any  other  special  forces  of  their  own. 

The  essence  of  cortical  function  is  correlation,  and  a  cortical 
center  for  the  performance  of  a  particular  function  is  a  physio- 
logical absurdity,  save  in  the  restricted  sense  described  above, 
as  a  nodal  point  in  a  very  complex  system  of  associated'  con- 


THE  FUNCTIONS  OF  THE  CEREBRAL  CORTEX      333 

duction  paths.  Those  reflexes  whose  simple  functions  can  be 
localized  in  a  single  center  have  their  mechanisms  abundantly- 
provided  for  in  the  brain  stem.  The  cerebral  cortex  of  the 
resting  brain  is  probably  in  a  state  of  incessant  activity,  i.  e., 
it  possesses  a  certain  physiological  ''tone."  This  activity 
may  be  conceived  as  a  system  of  equilibrated  nervous  dis- 
charges. This  is  not  necessarily  a  conscious  process,  but  it 
has  a  characteristic  pattern  in  each  individual  which  lies  at 
the  basis  of  his  disposition  or  mental  type.  An  effective 
stimulus  disturbs  this  equilibrium  and  the  precise  effect  will 
depend  upon  variable  synaptic  resistance  or  neuron  thresholds 
which  change  with  different  functional  states  of  the  organism 
as  a  whole  and  of  the  brain  in  particular.  If  this  activity 
involves  the  cerebral  cortex  of  a  human  brain,  it  may  be  a 
conscious  activity,  the  kind  of  consciousness  depending  on  the 
kind  of  discharge.  But  the  consciousness  must  not  be  thought 
of  as  localized  in  any  cortical  area.  The  discharge  in  question 
may  reverberate  to  the  extreme  limits  of  the  nervous  system 
and  the  peripheral  activities  may  be  as  essential  in  deter- 
mining the  conscious  content  as  the  cortical. 

Literature 

VON  Bechterew,  W.  1911.  Die  Funktionen  der  Nervencentra,  vol. 
iii,  Jena. 

Brown,  T.  Graham,  and  Sherrington,  C.  S.  1913.  Note  on  the 
Functions  of  the  Cortex  Cerebri,  Proc.  Physiol.  Soc.  for  March  15,  1913, 
Jour.  Physiol.,  vol.  xlvi. 

Burnett,  T.  C.  1912.  Some  Observations  on  Decerebrate  Frogs, 
with  Special  Reference  to  the  Formation  of  Associations,  Amer.  Jour. 
Physiol.,  vol.  xxx,  pp.  80-87. 

Gushing,  H.  1908.  Removal  of  a  Subcortical  Cystic  Tumor  at  a 
Second-stage  Operation  Without  Anesthesia,  Jour.  Amer.  Med.  Assoc, 
1908,  vol.  i,  p.  847. 

— .  1909.  A  Note  upon  the  Faradic  Stimulation  of  the  Postcentral 
Gyrus  in  Conscious  Patients,  Brain,  vol.  xxxii,  pp.  44-54. 

Edinger,  L.  1893.  The  Significance  of  the  Cortex^  Considered  in 
Connection  with  a  Report  Upon  a  Dog  from  which  the  Whole  Cerebrum 
had  been  Removed  by  Professor  Goltz,  Jour.  Comp.  Neurol.,  vol.  iii, 
pp.  69-77. 

— .  1908.  The  Relations  of  Comparative  Anatomy  to  Comparative 
Psychologv,  Jour.  Comp.  Neurol.,  vol.  xviii,  pp.  437-457. 

Edingeii,  L.,  and  Fischer,  B.  1913.  Ein  :Mensch  ohne  Grosshirn, 
Arch.  f.  ges.  Physiol,  Bd.  152.  pp.  1-27. 

Flechsig,  P.     1896.     Gehirn  und  Seele,  Leipzig. 


334  INTRODUCTION    TO    NEUROLOGY 

Flechsig,  p.     1896.     Die  Lokalisation  der  geistigen  Vorgange,  Leipzig. 

Franz,  S.  I.  1915.  Variations  in  Distribution  of  the  Motor  Centers, 
Psychological  Monographs,  Princeton,  N.  J.,  vol.  xix,  No.  1,  pp.  80-162. 

Fritsch,  G.,  and  Hitzig,  E.  1870.  Ueber  die  elektrische  Erregbar- 
keit  des  Grosshirns,  Arch.  f.  Anat.,  Physiol,  u.  Wissen.  Med.,  p.  300. 

Gall,  F.  J.     1825.     Sur  les  fonctions  du  cerveau,  6  vols.  Paris. 

GoLTZ,  F.  1869.  Beitrage  zur  Lehre  von  den  Functionen  der  Nerven- 
centren  des  Frosches,  Berlin. 

— .  1892.  Der  Hund  ohne  Grosshirn,  Arch.  f.  ges.  Physiol.,  Bd.  51, 
p.  570. 

Grunbaum,  a.  S.  F.,  and  Sherrington,  C.  S.  1903.  Observations  on 
the  Physiology  of  the  Cerebral  Cortex  of  the  Anthropoid  Apes,  Proc.  Roy. 
Soc,  vol.  Ixxii,  p.  152. 

Head,  H.,  and  Holmes,  G.  1911.  Sensory  Disturbances  from  Cere- 
bral Lesions,  Brain,  vol.  xxxiv,  pp.  109-254. 

Herrick,  C.  L.  1910.  The  Equilibrium  Theory  of  Consciousness,  in 
The  Metaphysics  of  a  Naturalist,  Bui.  Sci.  Lab.  Denison  ITniversitv,  vol. 
XV,  pp.  12-22. 

Hitzig,  E.  1904.  Physiologische  und  klinische  Untersuchungen 
liber  das  Gehirn,  Berlin. 

Holmes,  G.  W.  1901.  The  Nervous  System  of  the  Dog  Without  a 
Forebrain,  Jour.  Physiol.,  vol.  xxvii. 

Karplus,  J.  P.,  and  Kreidl,  A.-  1914.  Ueber  Totalextirpationen 
einer  und  beider  Grosshirnhemispharen  an  Affen  (Macacus  rhesus). 
Arch.  f.  (Anat.  u.)  Physiol.,  H.  1-2,  p.  155. 

Lewandowsky,  M.  1907.  Die  Funktionen  des  zentralen  Nerven- 
systems,  Jena. 

Leyton,  a.  S.  F.,  and  Sherrington,  C.  S.  1917.  Observations  on 
the  Excitable  Cortex  of  the  Chimpanzee,  Orang-utan,  and  Gorilla, 
Quart.  Jour.  Exper.  Physiology,  vol.  xi,  pp.  135-222. 

Marie,  P.  1906.  Revision  de  la  Question  de  I'Aphasie,  Semain 
Medicale,  23  May. 

Meyer,  A.  1910.  The  Present  Status  of  Aphasia  and  Apraxia,  The 
Harvey  Lectures  for  1909-10,  New  York,  pp.  228-250. 

VON  MoNAKOW,  C.  1909.  Neue  Gesichtspunkte  in  der  Frage  nach 
der  Lokalisation  im  Grosshirn,  Zeits.  f .  Psychologie,  Bd.  54,  pp.  161-182. 

— .  1910.  Aufbau  und  Lokalisation  der  Bewegungen  beim  Menschen. 
Arbeiten  a.  d.  hirnanatom,  Institut  in  Zurich,  Bd.  5,  pp.  1-37;  also  in 
Bericht  tiber  den  IV  Kongress  f.  exp.  Psychologie  in  Innsbruck,  1910. 

^.  1913.  Theoretische  Betrachtungen  iiber  die  Lokalisation  in 
Zentralnervensystem,  insbesondere  im  Grosshirn,  Ergebnisse  der  Physiol., 
Bd.  13,  pp.  206-278. 

— .     1914.     Die  Lokalisation  im  Grosshirn,  Wiesbaden. 

MuNK,  H.  1800.  LTeber  die  Funktionen  der  Grosshirnrinde.  Ge- 
sammelte  Abhandl.,  2d  ed.,  Berlin. 

— .  1902.  Zur  Physiologie  der  Grosshirnrinde,  Arch.  f.  Physiol., 
1902. 

Prince,  M.     1914.     The  Unconscious,  New  York. 


CHAPTER  XXI 

THE  EVOLUTION  AND  SIGNIFICANCE  OF  THE  CERE- 
BRAL CORTEX 

At  the  conclusion  of  our  analysis  of  the  structure  and  func- 
tions of  the  nervous  system  it  will  be  of  interest  to  review  very 
briefly  a  few  topics  of  a  more  general  sort  related  to  our  theme, 
with  special  reference  to  the  significance  of  the  cerebral  cortex 
in  the  general  scheme  of  human  evolution  and  culture. 

For  the  purpose  of  our  analysis  animal  activities  may  be 
classified  under  three  heads  (see  p.  32) :  (1)  Innate  functions  of 
invariable  or  stereotyped  character  developed  through  natural 
selection  or  other  biological  processes,  whose  mechanism  is 
hereditary  and  common  (with  small  differences  only)  to  all 
members  of  a  race  or  species,  typified  by  reflex  action  and 
purely  instinctive  action;  (2)  variable  and  modifiable  functions, 
whose  pattern  is  determined  by  individual  experience  through 
which  the  innate  action  system  is  more  or  less  permanently 
altered,  intelligent  acts  and  the  reasoning  process  representing 
the  highest  forms  of  this  type,  though  the  lower  members  of 
this  series  are  not  necessarily  consciously  performed;  (3) 
acquired  automatisms,  or  individually  acquired  actions  which 
have  become  so  thoroughly  habitual  as  to  be  performed  quite 
as  mechanically  as  the  hereditary  reflexes.  Intelligently 
acquired  actions  which  have  finally  come  to  be  automatically 
and  even  unconsciously  performed  are  sometimes  designated 
"lapsed  intelligence,"  but  such  lapsed  intelligence  must  be  a 
purely  individual  acquisition.  There  is  no  evidence  that  auto- 
matisms of  this  sort  can  be  transmitted  in  heredity,  and, 
therefore,  they  can  play  no  part  directly  in  the  evolution  of 
instincts,  as  some  have  taught. 

The  first  and  second  of  the  types  of  action  above  distinguished 
appear  to  be  common  to  all  organisms,  though  their  relative 
importance  varies  enormously  from  species  to  species.     The 

335 


336  INTRODUCTION  TO  NEUROLOGY 

first  type  includes  the  reflexes  and  all  of  the  pure  instinct- 
actions,  that  is,  the  hereditary  component  of  the  commonly 
recognized  instincts  (p.  64).  There  is  no  clear  boundary 
between  reflexes  and  instinct-actions  as  just  defined.  These 
actions  may  be  exceedingly  complex  and  their  neuro-muscular 
mechanisms  may  be  complicated  apparently  without  limit. 
The  available  evidence  suggests  that  they  are  always  uncon- 
sciously performed. 

Most  of  our  common  activities  include  all  three  of  these 
types  of  behavior  in  varying  proportions,  and  accordingly  they 
frequently  have  not  been  distinguished.  The  first  and  third 
types  are  especially  liable  to  confusion,  for  both  are  mani- 
fested as  stereotyped,  non-intelligent  behavior.  They  can 
sometimes  be  separated  only  by  a  study  of  their  origins;  never- 
theless this  distinction  is  of  great  importance,  especially  to 
educators. 

The  nervous  organs  of  the  invariable  reactions  are  fairly  well 
known  and  are  characterized  in  their  more  highly  elaborated 
forms  by  a  closely  knit  system  of  nerve-centers  and  distinct 
connecting  fiber  tracts  so  organized  that  particular  stimuli 
may  call  forth  a  response  or  a  combination  of  several  responses 
selected  from  a  fixed  number  of  possible  actions.  The  range 
of  possible  reactions  of  any  given  functional  system  of  this 
type  is  limited  by  the  structural  complexity  of  the  nerve- 
centers  involved.  This  complexity  may  be  very  great,  with 
a  correspondingly  great  number  of  movements  necessary  to 
complete  the  reaction,  and  it  may  include  the  capacity  for 
discriminating  between  two  or  more  structurally  possible 
modes  of  response  by  means  of  variable  internal  functional 
states  of  the  nerve-centers.  But  in  all  of  these  cases  the  re- 
sponse is  finally  determined  within  rather  narrow  limits  by 
the  nature  of  the  stimuli  and  the  innate  structural  organi- 
zation not  only  of  the  nervous  organs,  but  of  the  body  as  a 
whole. 

In  some  cases  an  elaborate  nervous  reflex  or  instinctive  act 
may  involve  a  more  extensive  nervous  apparatus  than  is 
required  by  an  intelligent  act.  It  is  not  a  mere  question  of  the 
size  of  the  nervous  mechanisms  involved.  For  instance,  a 
comparison  of  the  brains  of  the  two  species  of  fishes  shown  in 


EVOLUTION    AND    SIGNIFICANCE    OF    CEREBRAL    CORTEX     337 

Fig.  139  shows  that  in  the  medulla  oblongata  of  these  rather 
closely  related  species  there  is  an  astonishing  difference  between 
the  size  of  certain  reflex  centers.  The  greater  size  of  the 
medulla  oblongata  of  Carpiodes  over  that  of  Hyodon  is  due 
almost  entirely  to  the  enlargement  of  the  centers  for  taste,  ^ 
and  these  reflex  centers  are  found  to  be  very  complex.  The  en- 
ormous increase  in  the  mass  and  complexity  of  arrangement  of 


medulla 
_-  oblongata- 


Fig.  139. — Illustrations  of  the  brains  of  two  rather  closely  allied  species 
of  fishes  showing  very  different  development  of  the  reflex  centers  of  the 
medulla  oblongata:  (1)  Hyodon  tergisus,  the  moon-eye,  (2)  Carpiodes  tumi- 
dus,  a  carp-like  species.      (After  C.  L.  Herrick.) 


the  gustatory  neurons  in  Carpiodes  does  not  imply  any  higher 
organization  from  the  standpoint  of  range  of  behavior  (see 
p.  19)  than  in  Hyodon.  The  apparatus  is  more  efficient  as  a 
means  of  sorting  out  food  particles  from  mud,  but  we  do  not 
rank  this  form  of  activity  very  high  in  our  scale  of  behavior. 
In  general,  in  the  execution  of  a  complicated  reflex  many 

^  For  an  analysis  of  this  gustatory  apparatus  in  fishes,  see  Herrick,  C. 
JuDsox.     The  Central  Gustatory  Paths  in  the  Brains  of  Bony  Fishes, 
Jour.  Comp.  Neurol.,  vol.  xv,  1905,  pp.  375-456. 
22 


338  INTRODUCTION  TO  NEUROLOGY 

interconnected  nerve-centers  are  so  arranged  that  they  dis- 
charge into  a  common  final  path  or  an  integrated  series  of  such 
coordinated  paths.  The  movements  involved  in  the  act,  if 
performed  at  all,  must  follow  in  a  definite  sequence  which  is 
structurally  predetermined  in  the  inborn  organization  of  the 
nerve-centers  concerned.  In  the  variable  type  of  response, 
on  the  other  hand,  the  association  centers  involved  are  so 
arranged  that  many  final  paths  leading  to  different  systems  of 
coordinated  motor  centers  diverge  from  a  single  center  of 
correlation.  Which  of  these  paths  will  be  taken  in  a  given 
reaction,  that  is,  which  of  several  possible  different  (or  even 
antagonistic)  movements  will  result,  will  be  determined  by 
variable  physiological  factors  of  internal  resistance  within  the 
correlating  system  (fatigue,  habit,  the  influence  of  memory 
vestiges,  etc.) ;  accordingly,  the  response  is  not  predetermined 
by  the  inborn  organization  of  the  apparatus. 

Definite,  well-established  reflexes  generally  follow  distinct 
nervous  pathways  between  sharply  limited  nerve-centers .  Be- 
tween these  centers  there  is  usually  found,  in  addition  to  the 
well  insulated  tracts  just  mentioned,  a  more  diffuse  and  loosely 
organized  entanglement  of  nerve-cells  and  fibers,  through 
which  nervous  impulses  may  be  more  slowly  transmitted  in  any 
direction.  Tissue  of  this  character  is  found  throughout  the 
entire  length  of  the  central  nervous  system,  and  in  some  places 
it  occupies  extensive  regions  (especially  in  the  medulla  oblon- 
gata and  upper  part  of  the  spinal  cord)  which  are  termed  the 
reticular  formation  (see  pp.  69,  138,  172). 

The  reticular  formation  is  the  parent  tissue  out  of  which  'the 
higher  correlation  centers  have  been  differentiated.  In  the 
spinal  cord  and  medulla  oblongata,  where  its  character  is  most 
clearly  seen,  it  receives  fibers  from  all  of  the  sensory  centers 
and  may  discharge  motor  impulses  into  efferent  centers  of  con- 
tiguous or  very  remote  regions.  In  the  higher  parts  of  the 
brain  the  elaborate  association  centers  of  the  thalamus  and 
cerebral  hemispheres  have  been  developed  from  such  a  primi- 
tive matrix,  and  these  centers  are  interconnected  by  similar 
undifferentiated  nervous  tissue. 

The  details  of  the  functional  connections  of  the  reflex  centers 
of  the  brain  stem  are  much  more  precisely  known  than  are 


EVOLUTION"    AND    SIGNIFICANCE    OF    CEREBRAL    CORTEX    339 

those  of  the  higher  correlation  centers  of  the  thalamus  and 
cerebral  cortex.  And,  m  fact,  it  is  essential  that  these  details 
be  fairly  well  understood  before  the  functions  of  the  higher 
centers  can  be  investigated;  for  all  nervous  impulses  which 
reach  these  higher  centers  must  first  pass  through  the  lower 
centers  and  there  be  combined  into  reflex  systems  or  otherwise 
correlated.  The  afferent  stimuli  which  reach  the  cerebral 
cortex  are  not  crude  sensory  impressions,  but  purposeful  reflex 
combinations,  often  including  sensory  data  from  several  dif- 
ferent sense  organs. 

The  nerve-centers  of  the  spinal  cord  and  brain  stem  in 
general  are  of  this  more  rigid  type,  the  internal  adjustments  of 
the  system  being,  for  the  most  part,  as  mechanically  deter- 
mined as  are  those  of  an  automatic  telephone  exchange.  The 
cerebellum  is  the  highest  member  of  this  series,  exerting  a 
regulatory  and  reinforcing  influence  upon  all  of  the  other 
members.  Nevertheless  the  cerebellum  adds  no  new  types 
of  reaction  or  combinations  of  reactions  to  those  of  the  brain 
stem;  its  cortex  shows  little  demonstrable  localization  of  differ- 
ent functions,  and  its  efferent  tracts  are  physiologically  related 
to  a  limited  number  of  pre-established  systems  of  motor  coor- 
dination in  the  brain  stem  and  spinal  cord.  In  all  of  these 
respects  the  contrast  between  the  cerebellar  cortex  and  the 
cerebral  cortex  is  very  striking. 

The  variable  or  individually  modifiable  type  of  reaction  is 
served  chiefly  by  the  cerebral  cortex  and  its  immediate  depend- 
encies, though  some  capacity  of  this  sort  is  found  in  the  brain 
stem,  as  shown  by  the  behavior  of  lower  vertebrates  which  lack 
the  cerebral  cortex.  This  type  of  reaction  is  genetically  related 
with  that  modifiabflity  ai'ising  from  variable  internal  physio- 
logical states  which  we  have  mentioned  as  present  in  the  reflex 
centers.  There  is  no  proof  that  the  simpler  forms  of  this  indi- 
vidually modifiable  behavior  are  conscious,  though  the  higher 
forms  are  certainly  so. 

The  cerebral  cortex  can  in  no  case  act  independently  of  the 
reflex  centers  of  the  brain  stem,  but  always  through  the  agency 
of  these  centers.  It  is  superposed  upon  them  much  as  the  cere- 
bellum is,  though  the  control  exerted  is  of  a  very  different  type. 
Here  there  is  a  very  elaborate  regional  differentiation  of  the 


340  INTRODUCTION  TO  NEUROLOGY 

cortex  with  an  infinite  complexity  of  associational  connections. 
The  efferent  pathways,  moreover,  are  not  physiologically 
homogeneous;  but  they  are  so  diversified  that  any  possible 
combination  of  the  organs  of  response  may  be  effected  by 
associations  within  the  cortex.  The  various  afferent  func- 
tional systems  enter  sharply  circumscribed  cortical  areas 
(the  sensory  projection  centers);  and  the  efferent  fibers  like- 
wise leave  the  cortex  from  functionally  defined  motor  areas, 
each  group  of  muscles  which  cooperate  in  definite  reaction 
complexes  (termed  synergic  muscles,  see  p.  36)  being  excited 
from  a  definite  part  of  the  motor  cortical  field,  whose  motor 
tract  is  anatomically  distinct  throughout  its  entire  further 
course  from  the  cortex  to  the  periphery.  Between  the  sensory 
projection  centers  and  the  motor  areas  are  interpolated  the 
association  centers,  artd  these  are  so  arranged  that  all  corre- 
lation, integration,  and  assimilation  of  present  sensory  impulses 
with  memory  vestiges  of  past  reactions  are  completed,  and  the 
nature  of  the  response  to  be  made  is  determined  before  the 
resultant  nervous  impulses  are  discharged  into  the  motor 
centers.  Only  such  of  the  motor  areas  will  be  excited  to 
function  as  are  necessary  for  evoking  the  particular  reaction 
which  is  the  appropriate  (that  is,  adaptive)  response  to  the 
total  situation  in  which  the  body  finds  itself.  This  arrange- 
ment of  association  centers  in  relation  to  a  series  of  distinct 
motor  areas  provides  the  flexibility  necessary  for  complex 
delayed  reactions  whose  character  is  not  predetermined  by  the 
nature  of  the  congenital  pattern  of  the  nervous  connections.^ 

The  thalamus,  as  we  have  seen  (p.  178)',  has  its  own  intrinsic  system  of 
association  centers  which  discharge  downward  into  the  cerebral  pedun- 
cles, and  this  is  the  primary  reflex  apparatus  of  this  part  of  the  brain. 
The  thalamo-cortical  connections  arose  to  prominence  later  in  the  evolu- 
tionary history,  though  feeble  rudiments  of  these  are  present  in  lower 
brains.  Parallel  with  the  enlargement  of  these  cortical  connections  a 
special  part  of  the  thalamus  was  set  apart  for  them,  and  from  the  Amphi- 
bia upward  in  the  animal  scale  this  dorsal  part  of  the  thalamus  assumed 
increasingly  greater  importance.  This  part  is  termed  by  Edinger  the 
neothalamus,  and  makes  up  by  far  the  larger  part  of  the  thalamus  in  the 
human  and  all  other  mammalian  brains.  It  occupies  the  dorso-lateral 
part  of  the  thalamus  proper  and  comprises  most  of  the  great  thalamic 

1  The  paragraphs  which  follow  (pp.  340-346)  are  reproduced  with  slight 
modification  from  The  Journal  of  Animal  Behavior,  vol.  iii,  1913,  pp. 
228-236. 


EVOLUTION-    AXD    SIGNIFICANCE    OF    CEREBRAL   CORTEX       341 

nuclei  Gateral  and  ventral  nuclei,  pulvinar  and  lateral  and  medial  genicu- 
late bodies).  The  primitive  intrinsic  reflex  thalamic  apparatus  in  man 
is  a  relatively  unimportant  area  of  medial  gray  matter  and  the  subthala- 
mic region  (corpus  Luysii,  lattice  nucleus,  etc.,  not  to  be  confused  with 
the  hypothalamus  which  lies  farther  down  in  the  tuber  cinereum  and 
mammillary  bodies). 

The  neothalamus,  accordingly,  serves  as  a  sort  of  vestibule  to  the  cor- 
tex, every  afferent  impulse  from  the  sensor}'  centers  (except  the  olfactory 
system)  being  here  interrupted  by  a  synapse  and  opportunity  offered  for 
a  wide  range  of  subcortical  associations.  The  olfactory  cortex  (hippo- 
campal  formation)  has  a  similar  relation  to  subcortical  correlation  centers 
in  the  olfactory  area  in  the  anterior  perforated  space,  septum,  etc. 

From  these  anatomical  considerations  it  follows  that  no  simple  sensory 
impulse  can,  under  ordinary  circumstances,  reach  the  cerebral  cortex 
without  first  being  influenced  by  subcortical  correlation  centers,  within 
which  complex  reflex  combinations  may  be  effected  and  various  automa- 
tisms set  off  in  accordance  with  their  preformed  structure.  These  sub- 
cortical systems  are  to  some  extent  modifiable  by  racial  and  individual 
experience,  but  their  reactions  are  chiefly  of  the  invariable  or  stereotj-ped 
character,  ^vith  a  relatively  limited  range  of  possible  reaction  types  for 
any  given  stimulus  complex. 

It  is  shown  by  the  lower  vertebrates  which  lack  the  cerebral  cortex  that 
these  subcortical  mechanisms  are  adequate  for  all  of  the  ordinan.'  simple 
processes  of  life,  including  some  degree  of  associative  memon,-.  But  here, 
when  emergencies  arise  which  involve  situations  too  complex  to  be 
resolvedby  these  mechanisms,  the  animal  will  pay  the  ine-\-itable  penalty 
of  failure — perhaps  the  loss  of  his  dinner,  or  even  of  his  life. 

In  the  higher  mammals  with  well-developed  cortex  the  reflexes 
and  simple  associations  are  likewise  performed  in  the  main  by  the  sub- 
cortical apparatus,  but  the  inadequacy  of  this  apparatus  in  any  particular 
situation  presents  not  the  certainty  of  failure,  but  rather  a  dilemma.  The 
rapid,  preformed  reflex  mechanisms  fail  to  give  relief,  or  perhaps  the  situa- 
tion presents  so  many  complex  sensory  excitations  as  to  cause  mutual 
interference  and  inhibition  of  all  reaction.  There  is  a  stasis  in  the  sub- 
cortical centers.  Meanwhile  the  higher  neural  resistance  of  the  cortical 
pathways  has  been  overcome  by  summation  of  stimuli  and  the  cortex  is 
excited  to  function.  Here  is  a  mechanism  adapted,  not  for  a  limited 
number  of  predetermined  and  immediate  responses,  but  for  a  much 
greater  range  of  combination  of  the  afferent  impressions  with  each  other 
and  with  memory  vestiges  of  previous  reactions  and  a  much  larger  range 
of  possible  modes  of  response  to  any  given  set  of  aft'erent  impressions.  By 
a  process  of  trial  and  error,  perhaps,  the  elements  necessary  to  effect  the 
adaptive  response  maj''  be  assembled  and  the  problem  solved. 

It  is  eA-ident  here  that  the  physiological  factors  in  the  dilemma  or  prob- 
lem as  this  is  presented  to  the  cortex  are  by  no  means  simple  sensory 
impressions,  but  definitely  organized  systems  of  neural  discharge,  each  of 
which  is  a  physiological  resultant  of  the  reflexes,  automatisms,  impulses, 
and  inhibitions  characteristic  of  its  appropriate  subcortical  centers. 
The  precise  form  wliich  these  subcortical  combinations  will  assume  in 
response  to  any  particular  excitation  is  in  large  measure  determined  by  the 
structural  connections  of  these  centers  inter  se.  And  the  pattern  of  these 
connections  is  tolerably  uniform  for  all  members  of  any  animal  race  or 
species.  This  implies  that  it  is  hereditary  and  innate.  This  is  the  under- 
lying basis  of  instinct. 


342  INTRODUCTION  TO  NEUROLOGY 

The  connections  between  the  cortical  centers,  on  the  other  liand,  are 
much  less  definitely  laid  down  in  the  hereditary  pattern.  The  details  of 
the  definitive  association  pattern  of  anyindividual  are  to  a  greater  degree 
fixed  by  his  particular  experience.  This  is  the  basis  of  docility  and  the 
individually  modifiable  or  intelligent  types  of  behavior.  The  typical  cor- 
tical activities,  even  when  physiologically  considered,  are  far  removed 
indeed  from  those  of  the  brain  stem. 

It  should  be  emphasized,  however,  that  the  differences  between  the  cor- 
tex and  the  lower  centers  of  the  brain  stem,  so  far  as  these  can  be  deduced 
from  a  study  of  structure  and  from  physiological  experimerit,  are  relative 
and  not  absolute.  Indeed,  the  general  pattern  of  the  regional  localiza- 
tion of  the  cortex  itself  is  innate,  and  in  adult  life  the  cortex  has  acquired 
many  more  characteristics  similar  to  those  of  the  brain  stem,  with  its  own 
systems  of  acquired  automatisms  and  habitually  fixed  types  of  response. 
The  larger  association  centers  retain  their  plasticity  longest,  but  ulti- 
mately these  also  cease  to  exliibit  new  types  of  correlation,  and  this  marks 
the  onset  of  senility. 

The  relations  of  the  cerebral  cortex  to  the  cerebellar  cortex  and  the 
brain  stem  have  been  compared  (p.  215)  to  those  of  an  enlarged  judicial 
branch  of  the  central  government  charged  with  the  duty  of  interpreting 
the  decrees  of  the  lower  legislative  centers  and  dominating  the  adminis- 
trative machinery,  and  with  the  additional  power  of  shaping  the  general 
policy  of  the  government. 

Dewey's  stimulating  analysis^  of  the  reflex  arc  concept  or,  as  he  pre- 
fers to  say,  the  organic  circuit  concept  implies  that  the  synthesis  of  the 
elements  of  a  complex  chain  reflex  into  an  organic  unity  is  the  essential 
prerequisite  of  that  apperceptive  process  which  will  make  the  total  experi- 
ence of  value  for  future  discriminative  responses— for  learning  by  experi- 
ence. This,  which  is  true  in  the  individual  learning  process,  is  also  true 
phylogenetically.  The  correlation  centers  (and  their  capacity  for  the 
preservation  of  vestiges  of  past  reactions)  are  the  organic  mechanism  for 
this  synthesis.  They  make  it  possible  that  a  new  stimulus  may  be  re- 
acted to,  not  as  a  detached  element,  but  as  a  component  of  a  complex  series 
of  past  and  present  adjustments,  to  which  it  is  assimilated  in  the  asso- 
ciation centers — apperception.  This  assimilation  or  apperceptive  proc- 
ess is  an  integral  part  of  the  receptor  process  in  the  higher  centers,  giv- 
ing the  quale  to  the  idea  of  the  exciting  object.  Contemporaneously  with 
this  stimulus-apperception  process  we  have  an  apperception-response- 
activity  giving  the  object-  or  purpose-idea,  so  that  the  entire  reaction  is 
to  be  regarded  as  stimulus-apperception-response,  as  a  functional  unity 
rather  than  as  a  sequence:  stimulus>apperception>response. 

Dewey's  organic  circuit  concept  is  elaborated  in  terms  of  psychology. 
Let  us  see  how  it  may  be  applied  to  biological  behavior. 

The  simple  reflex  is  commonly  regarded  as  a  causal  sequence:  given  the 
gun  (a  physiologically  adaptive  structure),  load  the  gun  (the  constructive 
metaboHc  process),  aim,  pull  the  trigger  (apphcation  of  the  stimulus),  dis- 
charge the  projectile  (physiological  response),  hit  the  mark  (satisfaction 
of  the  organic  need).  All  of  the  factors  may  be  related  as  members  of  a 
simple  mechanical  causal  sequence  except  the  aim.  For  this  in  our  illus- 
1  The  Reflex  Arc  Concept  in  Psychology,  Psych.  Rev.,  vol.  iii,  p.  357, 
1893.  See  also  Dewey's  later  statement  in  Jour.  Philos.,  Psych.,  and  Sci. 
Methods,  vol.  ix,  Nov.,  1912,  pp.  664-668,  especially  the  footnote  on  p. 
667. 


EVOLUTION    AND    SIGNIFICANCE    OF    CEREBRAL    CORTEX     343 

tration  a  glance  backward  is  necessary.  An  adaptive  simple  reflex  is 
adaptive  because  of  a  pre-established  series  of  functional  sequences  which 
liave  been  biologically  determined  by  natural  selection  or  some  other 
evolutionary  process.  This  gives  the  reaction  a  definite  aim  or  objective 
purpose.  In  short,  the  aim,  like  the  gun,  is  provided  by  biological  evolu- 
tion, and  the  whole  process  is  implicit  in  the  structure-function  organiza- 
tion which  is  characteristic  of  the  species  and  whose  nature  and  origin  we 
need  not  here  further  inquire  into. 

Now,  passing  to  the  more  complex  instinctive  reactions,  so  fa,r  a^  these 
arc  unconscious  automatisms,  they  may  be  elaborations  of  chain  reflexes 
of  the  type  discussed  above  (p.  64).  But  the  aim  (biological  purpose)  is 
so  inwrought  into  the  course  of  the  process  that  it  cannot  be  dissociated. 
Each  step  is  an  integral  part  of  a  unitary  adaptive  process  to  serve  a  defi- 
nite biological  end,  and  the  animal's  motor  acts  are  not  satisfying  to  him 
unless  they  follow  this  predetermined  sequence,  though  he  himself  may 
have  no  clear  idea  of  the  aim. 

These  reactions  are  typical  organic  circuits.  The  cycle  in  some  of  the 
instincts  of  the  deferred  type  comprises  the  whole  life  of  the  individual. 
In  other  cases  the  cycle  is  annual  (as  in  bird  migrations,  etc.),  diurnal,  or 
linked  up  with  definite  physiological  rhythms  (e.  g.,  the  nidification  of 
liirds  as  described  by  F.  H.  Herrick,  see  p.  64).  In  still  other  cases  there 
is  no  apparent  simple  rhythm.  But  always  the  process  is  not  a  simple 
sequence  of  distinct  elements,  but  rather  a  series  of  reactions,  each  of 
which  is  shaped  by  the  interactions  of  external  stimuli  and  a  preformedor 
innate  structure  which  has  been  adapted  by  biological  factors  to  modify 
the  response  to  the  stimuli  in  accordance  with  a  purpose,  which  from  the 
standpoint  of  an  outside  observer  is  teleological,  i.  e.,  adapted  to  conserve 
the  welfare  of  the  species. 

Every  intelligently  directed  response  to  external  stimulation  involves  a 
large  measure  of  highly  complex  unconscious  cerebration  of  this  type; 
and  it  is  possible  to  describe  with  considerable  precision  the  mechanisms 
of  the  subcortical  activities  involved  in  many  of  those  organic  circuits 
which  are  commonly  regarded  as  typically  cortical. 

Much  of  that  which  goes  in  psychological  literature  under  such  contra- 
dictory terms  as  unconscious  mind  or  subconscious  mind  is,  in  reality,  the 
subcortical  elaboration  of  types  of  action  system  which  ordinarily  do  not 
involve  the  cortex  at  all,  but  which  upon  occasion  may  be  linked  up  with 
cortical  associational  processes  and  then  come  into  consciousness  in  such 
a  form  as  to  suggest  to  introspection  that  they  are  all  of  a  piece  with  the 
conscious  process  with  which  they  are  related.  _  In  fact,  within  the  cortex 
itself  there  are  doubtless  many  rotitine  activities  which  do  not  ordinarily 
come  into  consciousness,  particularly  of  the  sort  known  as  acquired 
juitomatisms  or  lapsed  intelligence;  and  these,  though  of  quite  different 
origin  from  the  innate  instinctive  systems,  cannot  easily  be  distinguished 
from  them  in  the  form  in  which  they  are  experienced  in  the  adult. 

In  the  organic  circuit  as  defined  by  Dewey  the  process  is  considered  as 
a  whole,  so  that  the  response  is  conceived  as  logically  implicit  in  the  stim- 
ulus. The  motor  reaction,  he  says,  is  not  merely  to  the  stimulus;  it  is 
into  the  stimulus.  "  It  occurs  to  change  the  sound,  to  get  rid  of  it.  What 
we  have  is  a  circuit,  not  an  arc,  or  broken  segment  of  a  circle.  This 
circuit  is  more  truly  termed  organic  then  reflex,  because  the  motor  re- 
sponse determines  the  stimulus  just  as  truly  as  sensory  stimidus  deter- 
mines movement."     This  notion,    which  is  difficult   for  the  practical 


344 


INTRODUCTION"   TO   NEUROLOGY 


scientific  mind  to  understand,  is  considerably  clarified  by  some  neurolog- 
ical considerations. 

From  the  standpoint  of  the  cerebral  cortex  considered  as  an  essential 
part  of  the  mechanism  of  higher  conscious  acts,  every  afferent  stimulus,  as 
we  have  seen,  is  to  some  extent  affected  by  its  passage  through  various 
subcortical  correlation  centers  (i.e.,  it  carries  a  quale  of  central  origin). 
But  this  same  afferent  impulse  in  its  passage  through  the  spinal  cord  and 
brain  stem  may,  before  reaching  the  cortex,  discharge  collateral  impulses 


Fig.  140. — Diagram  of  the  relation^  of  tfie  pyramidal  tract  in  a  rabbit  or 
similar  lower  mammalian  brain.  Sensory  stimuli  enter  the  spinal  cord  from 
the  skin  through  the  peripheral  sensory  neuron,  »S,  and  ascend  to  the  cerebral 
cortex  through  the  lemniscus,  L.  The  descending  pyramidal  tract,  P,  lies 
in  the  dorsal  funiculus  of  the  spinal  cord.  Its  intercalary  neuron,  I,  may  be 
stimulated  by  both  the  peripheral  neuron,  S,  and  by  the  pyramidal  tract,  P. 
It  discharges  upon  the  peripheral  motor  neuron,  M. 

into  the  lower  centers  of  reflex  coordination,  from  which  incipient  (or 
even  actually  consummated)  motor  jesponses  are  discharged  previous 
to  the  cortical  reaction.  These  motor  discharges  may,  through  the  ' '  back 
stroke"  action,  in  turn  exert  an  influence  upon  the  slower  cortical  reaction. 
Thus  the  lower  reflex  response  may  in  a  literal  physiological  sense  act  into 
the  cortical  stimulus  complex  and  become  an  integral  part  of  it. 

But  there  is  another  aspect  of  the  problem  which  has  receritly  been 
brought  to  our  notice  by  Kappers.^     It  is  a  well-known  fact,  which  is  not 

1  Kappers,  C.  U.  AmiiNS.  Ueber  die  Bildung  von  Faserverbindungen 
auf  Grund  von  simultanen  und  sukzessiven  Reizen.     Bericht  fiber  den 


EVOLUTION    AND    SIGNIFICANCE    OF    CEREBRAL    CORTEX       345 

often  taken  ticcoimt  of  in  this  connection,  that  the  descending  cortical  paths 
(pyramidal  tracts)  do  not  typically  end  directly  upon  the  peripheral  mortor 
neurons  whose  functions  they  excite,  but  rather  upon  intercalary  neurons 
which  lie  in  the  reticular  formation  or  even  in  the  adjacent  sensory 
centers.  These  intercalary  neurons,  in  turn,  excite  the  peripheral  motor 
neurons.  The  same  intercalary  neuron  which  receives  the  terminals  of 
the  pyramidal  tract  also  receives  collaterals  from  the  peripheral  sensory 
neurons  of  its  own  segment  (Fig.  140).  This  arrangement  is  the  explana- 
tion of  the  fact  that  the  pyramidal  tract  fibers  descend  through  the  human 
spinal  cord  for  the  most  part  in  the  dorso-lateral  region,  not  in  the  ventral 
funiculus  like  most  other  motor  tracts.  In  most  lower  mammals  the 
pyramidal  tract  actvially  descends  within  the  dorsal  funiculus  in  the 
closest  possible  association  with  the  peripheral  sensory  fibers,  and  this 
arrangement  is  clearly  the  primitive  relation  of  the  descending  cortical 
pathway. 

Accordingly,  stimulation  of  the  skin  of  the  body  excites  a  dorsal  spinal 
root  fiber  which  ascends  toward  the  cortex  within  the  spinal  cord  and  also 
gives  collateral  branches  to  intercalary  neurons  of  the  spinal  cord  itself. 
The  latter  neurons  may  excite  motor  elements  of  the  spinal  cord  to  an 
immediate  reflex  response  which  is  well  under  way  before  the  cortical 
return  motor  impulse  gets  back  to  the  spinal  cord  and  discharges  into 
these  same  intercalary  neurons  which  are  already  under  sensory  stimu- 
lation directly  from  the  periphery.  The  effect  of  this  arrangement  is 
that  the  central  motor  path  during  function  is  under  the  influence  of 
sensory  stimulation  at  both  ends,  and  is  not,  as  commonly  described, 
under  simple  sensory  stimulation  at  the  cortical  end  and  purely  emissive 
in  function  at  the  spinal  end. 

Viewed  from  the  standpoint  of  cerebral  dynamics,  the  exact  physiolog- 
ical effect  of  the  discharge  of  a  central  motor  bundle  such  as  the  pyra- 
midal tract  will  be  dependent  upon  the  combined  action  of  the  sensory 
stimulation  at  the  cortical  end  and  the  state  of  sensory  excitation  at  the 
spinal  end,  as  well  as  upon  the  resistance  of  the  motor  apparatus  itself. 

We  saw  in  a  previous  paragraph  how  the  simple  reflexes  of  the  spinal 
cord  may  become  factors  in  the  stimulus  complex  of  the  cortex.  Here  we 
find,  conversely,  that  the  efferent  cortical  discharge  may  become  a  factor 
in  the  local  reflex  stimulation  of  a  motor  spinal  neuron.  From  both 
standpoints  Dewey's  conception  of  the  unitary  nature  of  the  organic 
circuit,  as  contrasted  with  the  classical  reflex  arc  concept,  receives  strong 
support. 

The  thalamic  correlation  centers  probably  serve  as  the  organs  Tpar 
excellence  where  are  elaborated  those  organic  circuits  which  give  to  the 
higher  apperceptive  processes  of  the  cortex  that  quale  to  which  DeAvey 
refers.  The  origin  of  this  quale  is  to  be  sought  partly  in  the  subcortical 
assimilation  of  a  present  stimulus  complex  to  the  pre-existing  organic 
circuits  structurally  laid  down  in  the  reflex  mechanism,  and  partly  in  an 
affective  quality  pertaining  to  the  several  organic  circuits  involved  in  the 
reaction.     This  affective  quality  may  be  innate  or  it  may  have  been 

III  Kongress  fiir  experimentelle  Psychologie  in  Frankfurt  a.  Main,  1908. 
Mso  Weitere  Mitteilungen  uber  Neurobiotaxis.  Folia  Neuro-Biologiea, 
Bd.  I,  No.  4,  April,  1908,  pp.  507-532. 

See  also  Dearborn,  G.  V.  N.  Kinesthesia  and  the  Intelligent  Will, 
Amer.  Jour,  of  Psychol,  vol.  xxiv,  1913,  pp.  204-255. 


346  INTRODUCTION  TO  NEUROLOGY 

acquired  by  experience  of  the  results  of  previous  reactions  of  the  sort  in 
question. 

Head  and  Holmes  have  brought  forward  some  very  interesting  evidence 
that  not  only  the  affective  quale  of  sensations  but  also  the  emotional  life 
in  general  is  functionally  related  to  the  primitive  intrinsic  nuclei  of  the 
thalamus,  rather  than  to  cortical  activity  (see  p.  282).  And  certainly 
there  is  much  evidence  in  the  behavior  of  lower  animals,  especially  birds, 
that  a  high  degree  of  emotional  activity  is  possible  where  the  basal  centers 
are  highly  elaborated  but  the  cerebral .  cortex  is  small  and  very  simply 
organized. 

From  all  of  these  considerations  it  seems  probable  that  the  functions  of 
the  higher  association  centers  of  the  cerebral  cortex  do  not  consist  of  the 
elaboration  of  crude  sensory  data  or  of  any  similar  elements,  but  rather  of 
the  assembling  and  integration  of  highly  elaborated  subcortical  organic 
circuits  which  in  the  aggregate  make  up  the  greater  part  of  the  reflex  and 
instinctive  life  of  the  species. 

The  functions  of  the  cerebral  cortex  fall  into  two  great 
groups:  (1)  Correlations  of  great  complexity,  i.  e.,  with  many 
diverse  factors.  This  is  of  no  practical  value  without  ca- 
pacity for  choice  between  many  possible  different  reactions  to 
the  situation.  This  "  switch-board  "  type  of  function  is  simply 
a  higher  elaboration  of  the  physiological  patterns  of  the  lower 
correlation  centers,  (2)  Retentiveness  of  past  individual  im- 
pressions in  such  form  as  to  permit  of  subsequent  recall  and 
incorporation  into  new  stimulus  complexes.  This  mnemonic 
function  is  simply  a  higher  elaboration  of  primitive  proto- 
plasmic "organic  memory"  or  individual  modifiability.  The 
mechanism  of  the  first  group  of  functions  may  be  largely 
innate  and  heritable;  that  of  the  second  is  necessarily  individu- 
ally acquired.  These  two  functions  lie  at  the  basis  of  all 
7nind. 

The  normal  newborn  child  brings  into  the  world  an  in- 
herited form  of  body  and  brain  and  a  complex  web  of  nerve- 
cells  and  nerve-fibers  which  provide  a  fixed  mechanism,  com- 
mon except  for  minor  variations  to  all  members  of  the  race 
alike,  for  the  performance  of  the  reflex  and  instinctive  actions. 
The  pattern  of  this  hereditary  fabric  can  be  changed  only  very 
slowly  by  the  agency  of  selective  matings  and  other  strictly  bio- 
logical factors  or  by  degenerations  of  a  distinctly  pathological 
sort.  It  is  thus  manifest  that  the  improvement  of  the  racial 
stock  of  normal  individuals  by  the  practice  of  eugenics  must 
necessarily  be  very  slow,  though  the  improvement  of  defective 
or  pathological  strains  by  selective  matings  so  as  to  breed  out 


EVOLmON    AND    SIGNIFlOANfE    OF    CEREBRAL    CORTEX       347 

the  objectionable  characteristics  is  fortuiialc^ly  in  most  cases 
more  rcadil}^  accomplished. 

But  in  addition  to  this  hereditary  organization  the  newi^orn 
child  possesses  the  large  association  centers  of  the  brain  with 
their  vast  and  undetermined  potencies,  the  exact  form  of  whose 
internal  organization  is  not  wholly  laid  down  at  birth,  ])ut  is 
in  part  shaped  by  each  individual  separately  during  the  course 
of  the  growth  period  by  the  processes  of  education  to  which  he 
is  subjected,  that  is,  by  his  experience.  This  capacity  for  indi- 
viduality in  development,  this  ability  to  profit  by  experience, 
this  docility,  is  man's  most  distinctive  and  valuable  character- 
istic. And  since  the  form  which  this  modifiable  tissue  will  take 
is  determined  by  the  environing  influences  to  which  the  child 
is  subjected,  and  since  these  influences  are  largely  under  social 
control,  it  follows  that  human  culture  can  advance  by  leaps 
and  bounds  wherever  a  high  level  of  community  life  and  edu- 
cational ideals  is  maintained. 

So  well  have  we  learned  the  lesson  that  the  child  brings  with 
him  into  the  world  no  mental  endowments  ready-made— no 
knowledge,  no  ideas,  no  morals — but  that  these  have  to  be 
developed  anew  in  each  generation  under  the  guiding  hand  of 
education,  that  we  devote  one-third  of  the  expected  span  of  life 
of  our  most  promising  youth  to  the  educational  training  neces- 
sary to  ensure  the  highest  possible  development  of  the  latent 
cultural  capacities  of  these  association  centers  of  the  cerebral 
cortex. 

But  we  have  often  been  blind  to  the  other  side  of  the  picture. 
We  have  seen  above  that  the  adult  cortex  cannot  function  save 
through  the  reflex  machinery  of  the  brain  stem,  and  it  must  not 
be  forgotten  in  our  pedagogy  that  this  relation  holds  in  a  much 
more  vital  and  significant  sense  in  the  formative  years  of  the 
child.  It  is  true  that  the  child  is  born  with  no  mental  endow- 
ments; but  how  rich  is  his  inheritance  in  other  respects!  He 
has  an  immense  capital  of  preformed  and  innate  ability  which 
takes  the  form  of  physiological  vigor  and  instinctive  and  impul- 
sive actions,  performed  for  the  most  part  automatically  and 
unconsciously.  This  so-called  lower  or  animal  nature  is  ever 
present  with  us.  In  infancy  it  is  dominant;  childhood  is  a 
period  of  storm  and  stress,  seeking  an  equilibrium  between  the 


348  INTRODUCTION  TO  NEUROLOGY 

stereotyped  but  powerful  impulsive  forces  and  the  controls  of 
the  nascent  intellectual  and  moral  nature;  and  in  mature  years 
one's  value  in  his  social  community  life  is  measured  by  the 
resultant  outcome  of  this  great  struggle  in  childhood  and 
adolescence.     This  struggle  is  education. 

The  answer  to  the  riddle  of  life,  however,  lies  not  in  a  success- 
ful attack  upon  the  native  innate  endowments  of  the  child.  No, 
that  would  be  unbiological  and  wasteful,  for  our  world  of  ideas 
and  morals  is  no  artificial  world  within  the  cosmos,  but  it  is  a 
natural  growth,  which  is  as  truly  a  part  of  the  cosmic  process  as 
are  ''ape  and  tiger  methods "  of  evolution.  No  higher  associa- 
tion center  of  the  human  brain  can  function  except  upon  mate- 
rials of  experience  furnished  to  it  through  the  despised  lower 
centers  of  the  reflex  type.  So  also,  no  high  intellectual,  es- 
thetic, or  moral  culture  can  be  reached  save  as  it  is  built  upon 
the  foundation  of  innate  capacities  and  impulses. 

We  are  gradually  learning  through  the  kindergarten  that  the 
most  economical  way  to  lead  a  child  into  the  realm  of  learning 
is  not  to  stamp  out  all  of  his  natural  interests  and  shut  him  up 
with  his  face  to  the  wall,  while  he  learns  by  rote  an  a-b-c  lesson 
which  is  neither  interesting  nor  useful.  On  the  contrary,  we 
accept  as  given  his  native  impulses  and  automatisms,  his  spon- 
taneous interests  and  his  overproduction  of  useless  movements, 
and  we  use  these  as  the  capital  with  which  we  set  the  young- 
sters up  in  the  serious  business  of  the  acquisition  of  culture.  B  ut 
how  does  it  happen  that  we  make  so  small  use  of  the  principles 
here  learned  in  the  later  years  of  the  child's  schooling? 

Not  all  of  the  instincts  with  which  man  is  by  nature  endowed 
come  into  function  in  a  sucking  babe  or  a  kindergarten  pupil. 
Childish  curiosity  is  our  strongest  ally,  if  only  we  can  use  it 
wisely,  throughout  the  whole  of  the  educational  career  from  in- 
fancy to  the  graduate  school.  Anger  is  a  mighty  passion  in 
childhood.  It  is  not  wise  to  eradicate  it  altogether;  rather 
keep  it,  though  under  curb,  for  there  are  times  when  real 
abuses  arise  which  require  that  the  man  know  how  to  hit  and 
to  hit  hard.  And  so  with  the  instincts  of  self-preservation,  of 
fear,  of  sex — these  all  have  their  parts  to  play  in  the  nobler 
works  of  life  and  are  by  no  means  to  be  eradicated.  The 
ascetic  ideal  of  mortification  of  the  flesh  as  a  means  of  grace  is 


EVOLUTION    AND    SIGNIFICANCE    OF    CKREBRAL    CORTEX      349 

fundamentally  wrong  in  principle.  Our  case  calls  for  no  Ijlinil, 
indiscriminate  attack  upon  the  world  and  the  flesh,  but  rather 
the  subjugation  and  discipline  of  these,  so  that  we  may  use 
them  effectively  in  our  attack  upon  the  devil. 

Conflict  is  inherent  in  the  cosmic  process,  at  least  in  the  bio- 
logical realm,  from  beginning  to  end.  There  is  the  struggle  for 
physical  existence  among  the  animals.  And  even  in  the  lower 
ranks  of  life  there  arises  also  the  struggle  within  the  individual 
between  stereotyped  innate  tendencies  or  instincts  and  individu- 
ally acquired  experience.  This  is  clearly  shown  by  experi- 
ments on  animals  as  low  down  as  the  Protozoa.  And  out  of 
this  inner  conflict  or  dilemma  intelligence  was  born.  With  the 
gradual  emergence  of  self-consciousness  in  this  process  arises 
the  eternal  struggle  with  self,  that  conflict  which  leads  to  the 
bitter  cry,  "When  I  would  do  good  evil  is  present  with  me." 
Conflict,  then,  lies  at  the  basis  of  all  evolution,  and  the  factors 
of  social  and  even  of  moral  evolution  can  be  traced  downward 
throughout  the  cosmic  process. 

The  social  and  ethical  standards,  therefore,  have  not  arisen 
in  opposition  to  the  evolutionary  process  as  seen  in  the  brute 
creation,  but  within  that  process.  And  our  immediate  educa- 
tional problem  is  the  elaboration  of  a  practicable  system  of 
public  instruction  which  can  use  to  the  full  the  enormous  dy- 
namic energy  in  the  hereditary  impulsive  and  instinctive  endow- 
ment of  the  child,  and  build  upon  this,  in  the  form  best  suited 
to  the  respective  capacities  of  all  the  separate  individuals,  a 
properly  ordered  sequence  of  studies  which  will  develop  the 
latent  capacities  of  each  pupil  and  ensure  a  vital  balance 
between  the  strong  blind  impulse  of  the  innate  nature  and  the 
acquired  intellectual,  esthetic,  and  moral  control. 

And  herein  lies  the  solution  of  the  problem  of  human  freedom, 
so  far  as  this  rests  within  our  own  control.  The  limits  of  one's 
powers  and  the  range  within  which  his  freedom  of  action  is  cir- 
cumscribed are  in  part  determined  by  his  hereditary  endow- 
ments and  by  environmental  influences  over  which  he  has  no 
control.  These  are  decreed  to  him  by  his  fate,  and  the  innate 
organization  of  the  nervous  system  is  the  chief  instrument  of 
this  fate.  But  man  differs  from  the  brute  creation  chiefly  in 
that  he  can  more  completely  control  his  own  environment  and 


350  INTRODUCTION    TO   NEUROLOGY 

thereby  to  that  extent  take  his  fate  into  his  own  hands;  in 
other  words,  he  can  enrich  his  own  experience  along  hnes  of 
his  own  selection.  To  some  extent  each  individual  can  do  this 
for  himself  through  self -culture;  but  to  ensure  the  best  results 
of  such  efforts  there  must  be  a  social  control  of  the  environ- 
ment as  a  whole  by  concerted  community  action.  Individual 
freedom  of  action  can,  therefore,  attain  its  highest  efficiency 
only  through  a  certain  amount  of  voluntary  renunciation  of  the 
selfish  interests  where  these  conflict  with  community  welfare. 
Ethical  ideals  and  altruism  are  as  truly  evolutionary  factors 
in  human  societies  as  are  the  elemental  laws  of  self-preser- 
vation and  propagation  of  the  species.^ 

To  return  now  to  the  developing  nervous  system,  we  note 
that  the  educational  period  is  limited  to  the  age  during  which 
the  association  centers,  whose  form  is  not  predetermined  in 
heredity,  remain  plastic  and  capable  of  modification  under 
environmental  influence.  Ultimately  even  the  cerebral  cortex 
matures  and  loses  its  power  of  reacting  except  in  fixed  modes. 
Its  unspecialized  tissue — originaUy  a  diffuse  and  equipotential 
nervous  meshwork — -becomes  differentiated  along  definite 
lines  and  the  fundamental  pattern  becomes  more  or  less  rigid. 
The  docile  period  is  past,  and  though  the  man  may  continue 
to  improve  in  the  technic  of  his  performance,  he  can  no  longer 
do  creative  work.  He  is  apt  to  say,  "The  dog  is  too  old  to 
learn  new  tricks."  Whether  this  process  occurs  at  the  age  of 
twenty  or  eighty  years,  it  is  the  beginning  of  senility.  And, 
alas,  that  this  coagulation  of  the  mental  powers  often  takes 
place  so  early !  Many  a  boy's  brains  are  curdled  and  squeezed 
into  traditional  artificial  molds  before  he  leaves  the  grades  at 
school.     His  education  is  complete  and  semle  sclerosis  of  the 

'  III  this  connection  reference  may  be  made  to  three  very  interesting 
public  addresses  recently  delivered  before  the  American  Society  of  Natu- 
ralists : 

Jennings,  H.  S.  1911.  Heredity  and  Personality,  Science,  N.  S.,  vol. 
xxxiv,  pp.  902-910. 

CoNKLiN,  Edwin  G.  1913.  Heredity  and  Responsibility,  Science, 
N.  S.,  vol.  xxxvii,  pp.  46-54.  (Se.e  also  the  last  chapter  of  this  author's 
l)ook  on  Heredity  and  Environment,  Princeton,  1915.) 

Parker,  G.  H.  1915.  The  Value  of  Zoology  to  Humanity :  The  Eu- 
genics Movement  as  a  Public  Service,  Science,  N.  S.,  vol.  xli,  No.  105.3, 
pp.  342-347. 


EVOLITTION"    AND    BIGNIFK^ANCE    OF    CKHKliRAL    CORTEX        351 

mind  litis  hcgun  by  the  time  he  lius  leu]-iic(l  his  hade.  l<'(;r. 
how  many  such  disasters  our  brick-yard  methods  in  the  public 
schools  arc  responsible  is  a  question  of  lively  interest. 

We  who  seek  to  enter  into  the  kingdom  of  knowledge  and  to 
continue  to  advance  therein  must  not  only  become  as  little 
children,  but  we  must  learn  to  continue  so.  The  problem  of 
scientific  pedagogy,  then,  is  essentially  this:  to  prolong  the  plas- 
ticity of  childhood,  or  otherwise  expressed,  to  reduce  the  in- 
terval between  the  first  childhood  and  the  second  childhood  to 
as  small  dimensions  as  possible. 


INDEX  AND  GLOSSARY 


The  references  are,  in  all  cases,  to  pages.  Numbers  referring  to  pages  upon  which  the 
item  is  figured  are  printed  in  black-faced  type.  Authors'  names  are  printed  in  small 
CAPITALS.  Brief  definitions  of  some  of  the  more  commonly  used  technical  terms  are  in- 
cluded in  this  Index;  for  fuller  descriptions  consult  the  pages  cited.  Terms  which  are 
defined  in  this  Glossary  are  printed  in  black-faced  type.  The  names  of  fiber  tracts,  in 
general,  define  their  connections,  the  first  part  of  the  compound  word  indicating  the 
nucleus  of  origin  and  the  last  part  the  terminal  nucleus  (see  pages  117,  139).  To 
facilitate  cross-reference,  the  key-word  of  a  polynomial  term  is  capitalized  wherever 
it  occurs  in  this  Index  and  Glossary. 

Tables  of  synonyms  of  most  anatomical  names  will  be  found  in  the  works  by  Krause 
and  Eycleshymer,  cited  on  pages  134,  135. 


Accommodation  of  vision,  155,  231, 
235,  257,  261,  274 

AcHucARRo,  N.,  39,  58 

Acids,  sensitiveness  to,  77,  96,  270 

Acipenser  rubicundus,  nervous  svs- 
tem  of,  165,  166 

Acoustic  apparatus.  See  Auditory 
apparatus 

Acoustico-lateral  apparatus,  tlie 
nervous  mechanisms  of  the  in- 
ternal ear  and  lateral  line  organs 
in  fishes  and  amphibians.  See 
Nerves,  lateral,  and  Organs,  lat- 
eral line 

Action.     See  Behavior  and  Reflex 

Action  current,  102 

Action  system,  21,  32,  71 

Adrenalin  (epinephrin),  258,  283, 
284 

Affection,  affective  experience,  af- 
fective tone,  pleasure-pain,  emo- 
tions, and  allied  phenomena;  cf. 
Feeling  tone  and  Pain,  95,  182, 
268,  277-290,  345 

Affective  tone.  See  Feeling  tone 
and  Affection 

Afferent,  conducting  toward  a  cen- 
ter, 26,  44,  116,  137,  148 

Agraphia,  loss  of  the  power  to  write 
correctly,  326 

Agreeable  and  disagreeable.  See 
Affection 

Ala  cinerea  (vagal  eminence,  emi- 
nentia  vagi,  trigonum  vagi),  an 
23  353 


eminence  in  the  floor  of  the 
fourth  ventricle  formed  by  the 
dorsal  Nucleus  of  the  vagus,  168, 
170,  179,  261,  271 

Ala  lobulis  centralis,  210 

Alcohol,  sensitiveness  to,  270 

Alexia,  loss  of  the  power  of  reading 
(word-blindness),  326 

Altruism,  350 

Alveus,  association-fibers  which 
connect  the  Hippocampus  with 
the  Gyrus  hippocampi,  245,  246 

Ameboid,  resembling  an  ameba; 
applied  to  the  supposed  outward 
and  inward  movement  of  proc- 
esses of  cells  during  nervous 
function.  111 

Ameiurus  melas,  gustatorj'  nerves 
of,  273 

Amnion's  horn.     See  Hippocampus 

Amphibia,  nervous  svstem  of,  199, 
293 

Ampulla,  of  semicircular  canal, 
201,  218 

Amj^gdala.  See  Nucleus  amyg- 
dalae 

Anatomy  of  nervous  sj'Stem,  gen- 
eral, 114 

Andre-Thoma.s,  209,  216 

Anemia,  effect  on  nerve  cells,  252 

Anger.  See  also  Affection,  95,  283, 
284,  348 

Anguis  fragilis,  parietal  eye  of,  236, 
237 


354 


INDEX    AND    GLOSSARY 


Animals,    contrasted   with   plants, 

23 
Anterior,    as   used    in    this   work, 
means  toward  the  head  end  of 
•  the  body;  as  used  in  the  B.  N.  A. 
tables  it  means  toward  the  ven- 
tral side,  125 
Apathy,  S.,  58 
Apes,  nervous  system  of,  315,  316, 

324,  328 
Aphasia,  a  speech  defect  due  to  a 
cortical  injury,  or  more  broadly 
any  defect  in  symbolizing  rela- 
tions; cf.  Speech,  apparatus  of, 
325-327 
Aphemia,  loss  of  the  power  to  utter 

words,  326 
Apoplexy,  327 
Apperception,  277,  330,  342 
Appetite,  268 

Aqueduct   of   Sylvius    (iter,    opto- 
coele,  mesocoele),  the  ventricle  of 
the  midbrain,  65,  130,  175,  176 
Arachnoid,  the  middle  brain  mem- 
brane, 133 
Arbor  vitae,  the  tree-like  appear- 
ance of  the  white  matter  of  the 
cerebellum  in  section,  212 
Archipallium,  the  olfactory  cerebral 
cortex,  including  the  Hippocam- 
pus and  the  Gyrus  hippocampi 
Un  part),  241,  246,  306,  318,  322, 
341 
Area,  acoustic.     See  Area,  acous- 
tico-lateral,  Nucleus,  cochlear, 
and  Nucleus,  vestibular 
acoustico-lateral    (in   fishes  =  tu- 
berculum     acusticum),     119, 
120,  132,  155,  163,  166,  206, 
223 
cortical,  as  used  in  this  work  is  a 
part    of    the    cerebral  cortex 
which    can   be    differentiated 
from  its  neighbors  structurally 
by    the   arrangement    of    its 
cells    and    fibers    (sometimes 
termed     field) ;     cf.     Center, 
cortical,  305,  306,  320,  321,  322 
cutaneous,  119,  120,  132,  171 
general    somatic    sensory.     See 

Area,  cutaneous 
olfactoria,   the    region    contain- 
ing   the    secondary   olfactory 
centers,  divided  into  anterior, 


medial,      intermediate      and 
lateral    olfactory  Nuclei,  180, 
183,  239,  242,  243,  244,  245, 
341 
parolfactoria  of  Broca  (gyrus  ol- 
f  actorius  medialis  of  Retziu.s,  ) 
a  portion  of  the  medial  Area 
olfactoria  immediately   in 
front  of  the   Gyrus  subcallo- 
sus,  128 
perforata.     See  Substantia  per- 
forata 
somatic,  a  small  region  in  the  fish 
brain  from  which  the  Neopal- 
lium and  Corpus  striatum  were 
developed,  119,  120,  132 
striata,  that  part  of  the  occipital 
lobe  of  the  cerebral  cortex  con- 
taining the  Line  of  Gennari; 
the  visual  center,  297,  318 
visceral.      See    also    Lobe,    vis- 
ceral, 119,  120,  132,  162,  163, 
166, 167, 170, 264,  267,  274,  337 
Arteries,  nerves  of.    See  Vasomotor 

apparatus 
Articulates,  behavior  of,  33 
Association,  correlation  involving  a 
high  degree  of  modifiability  and 
also  consciousness,  37,  67,   110, 
269,  311,  325-331,  341 
Association    center.     See    Center, 
association 
fibers.     See    Fiber,    association, 

and  Tract,  association 
of  ideas,  329 
pattern,  325 
time  of,  104 
Asthma,  265 

Ataxia,  loss  of  the  power  of  mus- 
cular coordination,  148,  149 
Atropin,  258 
Attention,  109,  111 
Auditor}^  apparatus,  63,  65,  70,  75, 
92,  159,  161,  164,  171,  178,  180, 
183,  217-227         _      ^ 
Auditory  reaction  time,  104 
AuERBACH,    plexus   of    (myenteric 

plexus),  268 
Aula,  the  anterior  end  of  the  third 
ventricle  where  it  communicates 
with  the  lateral  ventricles  by 
way  of  the  interventricular  For- 
amina 
Auricle,  of  external  ear,  217 


INDEX    AND    GLOSSARY 


355 


Automatisms,  acquired,  33,  3(1, 
59,  320,  335,  343 

Avalanche  conduction.  See  Con- 
duction, avalanche 

Axis-cylinder,  the  central  proto- 
plasmic strand  of  a  nerve-filler; 
part  of  the  Axon,  41 

Axon  (axis-cylinder  process,  neiu-- 
ite,  neuraxon,  Neuraxis),  a  proc- 
ess of  a  Neuron  -which  conducts 
impulses  awav  from  the  cell 
body,  41,  45,  46,  47 

Axon  hillock,  the  point  of  origin  of 
an  axon  from  the  Cell  body,  41, 
42,  47 

Axone.     See  Axon 


Back-stroke,  the  influence  which  a 
peripheral  organ  of  response 
exerts  back  upon  the  center  from 
which  the  response  was  excited  : 
a  form  of  chain  Reflex ;  cf .  Reflex 
circuit,  2S9,  343 
Baillarger,    layer   of,    stripe   of. 

See  Line  of  Baillarger 
Bar,  terminal,  220 
B.iR.ixY,  R..  209,  216 
Barker,  L.  F.,  13,  38.  41,  52,  58, 

100,  153,  174,  248 
Bartelmez,  G.  W.,  56,  199 
Basis    pedunculi    (pes    peduncuH, 
crusta),  the  ventral  part  of  the 
cerebral  Peduncle,  composed  of 
descending  fiber  tracts,  123 
Basle    nomina  anatomica    (B.    N. 

A.),  124,  125,  130,  131 
Bechterew,  W.,  174,  237.  333 
Bechterew,  vestibular  nucleus  of, 

202,  203 
Behavior,   invariable,    activities 
whose  character  is  determined 
by  innate  structure,   typified 
by  reflex  and  instinctive  ac- 
tions, 32,   72,  S3,  84,  103,  198, 
292,  328,   335-338,  346 
range  of,  19,  337 
variable,    activities    which    are 
modifiable   by   individual  ex- 
perience, with  or  without  con- 
sciousness, 32,  67,  72.  83,  84, 
104,   107,   198,  292,  324,  328, 
335-338,  347,  349.  350 
Bell,  Charles,  83,  158,  174 


Bethe,  A.,  48,  58,  96 
Betweenbrain.     See  Diencephalon 
Betz,  cells  of.     See  Cells  of  Betz 
BiAxcHi,  A.,  216 
BiLLiNGSLEV,  P.  R.,  263,  276 
Birds,  behavior  of,  64,  343,  346 
olfactory  apparatus  of,  240 
thalamus  of,  182 
Black,  D.,  112,  113,  216 
Bladder,  innervation  of,  261,  257, 

270 
Blood,  coagulation  of,  283 
Blood-pressure,  110,  261 
Blood-Acssels,  nerves  of.     See  Cir- 
culation of  blood,  apparatus  of, 
and  Vasomotor  apparatus 
B.  X.  A.     See  Basle  nomina  ana- 
tomica 
Body,  of  cell.     See  Cell  body 
chromophilic.     See     Substance, 

chromophilic 
of  fornix.     See  Fornix  body 
geniculate,  lateral  (corpus  genic- 
ulatum     laterale,     external 
geniculate  body),   a   visual 
center    in     the    Thalamus, 
123,  164,  178,  179.  183,  232, 
234,  236,  318.  341 
geniculate,      medial      (corpus 
geniculatum  mediale,  internal 
geniculate  body),  an  auditory 
center  in  the  Thalamus,  123, 

127,  130,   168,   171,   178,   179, 
183,  203,  224,  225,  341 

habenular.     See  Habenula 

of  LuYs.  183,  341 

mammillary  (corpus  mamillare, 
corpus  candicans),  one  of  a 
pair  of  eminences  at  the  pos- 
terior end  of  the  Tuber  cine- 
rium  in  the  Hypothalamus ;  an 
olfactorv  center,  123,  129,  179, 
180,  181,  183,  234,  244,  341 

of  XissL.  See  Substance,  chro- 
mophilic 

pineal  (corpus  pineale.  pineal 
gland,  epiphysis,  conarium),  a 
glandular  outgrowth  from  the 
Epithalamus;  in  some  lower 
A-ertebrates  it  takes  the  form 
of  a  median  dorsal  eve.  See 
Parietal    eye,    118,    123,    127, 

128,  177,  178,  183,  23.- 
])ituitary.     See  Hypophysis 


356 


INDEX   AND    GLOSSARY 


Body,  quadrigeminal.    See  Corpora 
quadrigemina 
restiform.     See     Corpus     resti- 

forme 
striate.     See  Corpus  striatum 
tigroid.    See  Substance,  chromo- 

philic 
trapezoid    (corpus    trapezoid- 
eum),    transverse  decussating 
fibers  in  the  ventral  part  of  the 
medulla  oblongata  which  con- 
nect the  auditorjr  nuclei  of  one 
side  with  the  lateral  Lemnis- 
cus of  the  other  side,  52,  224 
BoLK,  L.,  208,  216 
Bolton,  J.  S.,  307,  309,  323 
Bonnet,  R.,  86 

Boring,  E.  G.,  88,  100,  189,  195 
Brachium,    of    colliculus    inferior. 
See  Brachium  quadrigeminum 
inferius 
conjunctivum  (^prepedunclej,  the 
superior  or  anterior  peduncle 
of  the  cerebellum;  cf.  Pedun- 
cle, cerebellar,  123,  142,  173, 
177,  194,  205 
pontis  (medipeduncle,  processus 
cerebelli  ad  pontem).  the  mid- 
dle peduncle  of  the  cerebellum ; 
cf.  Peduncle,  cerebellar,  123, 
131,  173,  177,  205,  206,  214 
quadrigeminum  inferius  (brach- 
ium  of  colliculus  inferior),   a 
ridge  on  the   Corpora  quadri- 
gemina formed  by  fibers  from 
the  Colliculus  inferior  to  the 
medial  geniculate  Body,  123, 
176,  179,  203 
Brain  (encephalon),  that  portion  of 
the    central    nervous    system 
contained  within  the  skull,  114 
development   of.     See    Nervous 

system,  development  of 
measurements  of,  132 
new.     See  Neencephalon 
nomenclature  of.     See  Nervous 

system,  nomenclature  of 
old.  See  Palaeencephalon 
stem,  all  of  the  brain  except  the 
cerebellum  and  the  cerebral 
corte.x  and  their  dependen- 
cies, i.  e.,  the  Segmental  ap- 
paratus, 122,  123,  124,  132, 
178,  198,  203,  204,  214 


Brain,  reflexes  of.     See  Reflexes  of 
brain  stem 
terminology    of.     See    Nervous 

system,  nomenclature  of 
weight  of,  132 
Branch.     See  Ramus 
Branchial  ganglia.     See  Ganglion, 
branchial 
nerves.     See  Gills,  innervation  of 
Bridge.     See  Pons 
Brooa,  p.,  326 
Broca's  area.     See  Area  parolfac- 

toria  of  Broca 
Broca's  convolution,  the  posterior 
part  of  the  gyrus  frontalis  in- 
ferior, supposed  to  function  as  a 
motor     correlation     center     of 
speech,  316,  326 
Brodmann,  K.,  306-309,  321 
Bronchial  tubes,  nerves  of,  265 
Brookover,  C,  240,  248 
Brouwer,  B.,  153,  189 
Brown,  Graham,  316,  333 
Bruce,  A.,  154 
Bruce,  A.  N.,  142,  154,  216 
Buchanan,  Florence,  104,  113 
Bulb  (bulbusj,  any  bulb-like  struc- 
ture; specifically  the  Medulla 
oblongata,  as  in  bulbar  paraly- 
sis, tractus  bulbo-spinalis 
olfactory,  a  protuberance  from 
the  cerebral  hemisphere  con- 
taining the  primary  olfactory 
center,  118,  119,  120,  129,  180, 
239,  241,  242,  243,  244,  293 
Bulbar  formation.     See  Formatio 

bulbaris 
Bundle.     See  Tract  and  Fasciculus 
basis,  fundamental,   or  ground. 

See  Fasciculus  proprius 
longitudinal   medial.     vSee   Fas- 
ciculus longitudinalis  medialis 
posterior  longitudinal.     See  Fas- 
ciculus longitudinalis  medialis 
solitary.     See  Fasciculus  solitar- 
ius 
Burdach,  column  of.     See  Fascic- 
ulus cuneatus 
BuRKET,  I.  R.,  253,  259 
burkholder,  j.  f.,  13 
Burnett,  T.  C.,  311,  333 

Cajal.     See  Ramon  y  Cajal 
Cajal,    commissural    nucleus    of. 


INDEX    AND    (iLOSSAUY 


3o7 


See    Nucleus,    coiiiniissural,    of 
Cajal 
Calcar  avis  (hippocampus  minor), 
a  projection  into  tlie  posterior 
horn    of    the    lateral   ventricle 
formed  by  the  calcarine  fissure 
Campbell,  A.  y\'.,  307,  309 
Canal,  central    (canalis  centralis), 
the  ventricle  of  the  spinal  cord, 
137,  140 
lateral  line.     See  Organs,  lateral 

line 
neural,  the  lumen  of  the  embry- 
onic Neural  tube ;  also  applied 
to  the  spinal  Canal  of  the  ver- 
tebral column 
semicircular    (ductus   semicircu- 
laris).     See  also  Vestibular  ap- 
paratus, 93,  118,  119,  201,  202, 
205,  217,  218,  223,  224 
spinal,  the  canal  in  the  vertebral 
column  containing  the  Spinal 
cord 
Cannon,  W.  B.,  268,  275,  283,  284, 

291 
Capps,  J.  A.,  278,  291 
Capsule,  external (capsula  externa), 
a    tliin    band    of    nerve-fibers 
forming  the  outer   border  of 
the  Corpus  striatum,  181,  184, 
186 
internal     (capsula     interna),     a 
strong    band    of    nerve-fibers 
passing    through    the    Corpus 
striatum,  123,   180,   181,   184, 
186,  191,  194,  234,  281,  296, 
321 
Capsule,  nasal,  118,  119 
Carbon  dioxid,   production  of,   in 
neurons,  102,  103,  109 
as  respiratory  stimulus,  266 
Carlson,  A.  J.,  268,  275 
Carp,  nervous  system  of,  47,  273, 

337 
Carpiodes  tumidus,  brain  of,  337 
Carr,  H.,  90,  100 
Carroll,  Robert  S.,  13 
Cat,  nervous  system  of,  95,  279 
Catfish,  nerves  of,  273 
Cauda   equina,  a   bvmdle  of  elon- 
gated spinal  nerve  roots  arising 
from  the  lumbar  and  sacral  seg- 
ments of  the  spinal  cord 
Caudal,  pertaining  to  the  tail,  or 


directed  toward  the  tail  I'ud  of 
1hc  body,  as  opposed  to  cephalic, 
125 
Cavum  septi  pellucidi  (fifth  ven- 
tricle, pseudocoele),  the  space  on- 
closed  between  the  Septa  pel- 
lucidaof  the  two  cerebral  hemi- 
spheres; not  a  true  ventricle, 
177 
Cell  (or  cells),  auditory  (hair  cells 

of  organ  of  Corti),  219,  220, 

221 
basket,  of  cerebellum,   54,  212, 

213,  214 
of  Betz  (giant  pyramidal  cells  of 

motor  center  of  cerebral  cor- 
tex), 302,  315,  316,  317 
body,  the  nucleus  and  perykary- 

on  of  a  neuron,  40 
of  Claudius,  221 
of  Corti  (hair  cells),  219,  220, 

221 
of  Deiters  of  organ  of  Corti, 

219,  221 
ependyma.     See  Ependyma 
granule,  of  cerebellar  cortex,  212, 
213,  214 

of  cerebral  cortex,   302,   306, 
308,  323 

of  olfactory  bulb,  242,  243 

of  retina,  230,  231 
of  Hensen,  221 
mitral,  an  olfactory  neurone  of 

the  second  order,  242,  243,  244 
nerve.     See  Neuron 
neuroglia.     See  Neuroglia 
olfactory,  97 
of    Purkin.te.     See    Purkinje, 

cells  of 
Cellulifugal,  conducting  away  from 
the    Cell   body,   applied    to   the 
processes  of  a  neuron 
Cellulipetal,  conducting  toward  the 
Cell  body,  applied  to  the  proc- 
esses of  a  neuron 
Center  (centrum),  a  collection  of 

nerve  cells  concerned  with  a 

particular  function,    26,    114, 

116,  117,  198,  336 
association.     See     also     Center, 

cortical,    association,    65,    66, 

104,   108,   109,   198,  286,  327, 

336,  340 
auditor  J- .     See    Area,    acoustic, 


358 


INDEX   AND    GLOSSARY 


Auditory  apparatus,  and  Cen- 
ter, cortical,  auditory 
correlation,   116,   117,  'l21,   129, 

144,  172,  198,  204,  340 
cortical,  a  part  of  the  cerebral 
cortex  which  can  be  differ- 
entiated functionallj^  from 
its  neighbors;  cf.  Area,  cor- 
tical. These  centers  are 
sometimes  called  areas, 
fields,  spheres,  or  zones,  306, 

315,  316,  323 
association,  199,  306,  318-333, 

340   345   346 

auditory,  181,  224,  225,  306, 
316 

gustatory,  274,  322 

motor,  71,  129,  151,  152,  198, 
305,  314,  315,  316,  317,  318, 
326,  340 

olfactory.     See  Archlpallium 

optic.  See  Center,  cortical, 
visual 

projection.  See  Projection 
center 

of  reading.  See  Speech,  ap- 
paratus of 

somesthetic,  181,  183,  281, 
305,  306,  315,  316,  317 

of  speech.  See  Speech,  appara- 
tus of 

tactile.  See  Center,  cortical, 
somesthetic 

of  temperature.  See  Center, 
cortical,  somesthetic 

visual,  183,  234,  297,  305,  308, 

316,  318,  322 

of  writing.     See   Speech,   ap- 
paratus of 
motor.     See    Motor    apparatus 

and  Center,  cortical,  motor 
optic.     See  Visual  apparatus  and 

Center,  cortical,  visual 
oval.     See  Center,  semioval 
for  pain.     See  Thalamus,  pain 

center  in 
primary,  117,  155,  165 
projection.     See  Projection  cen- 
ters 
reflex.     See  also  Reflex  circuit, 

117,  121,  140,  171 
respiratory,  264,  265-268 
Center,   semioval    (centrum  semi- 

ovale,    centrum     ovale),     the 


great  mass  of  white  matter  in 
the  center  of    each    cerebral 
hemisphere 
sensory,  129,  305 
tactile.     See    Area,    cutaneous, 
Touch,  apparatus  of,  and  Cen- 
ter, cortical,  somesthetic 
trophic,    a    nerve-center    which 
regulates  the  nutrition  of  an- 
other part,  117 
of  trunk  and  limb  reflexes,  140 
vasomotor.     See  Vasomotor  ap- 
paratus 
visceral.     See  Area,  visceral 
visual.      See    Visual    apparatus 
and  Center,  cortical,  visual 
Central  nervous  system.     See  Ner- 
vous system,  central 
pause,  104 
Centrifugal.     See  Efferent 
Centripetal.     See  Afferent 
Centrum.     See  Center 
Cephalic,  pertaining  to  the  head,  or 
directecl  toward  the  head  end  of 
the  body,  as  opposed  to  caudal, 
125 
Cerebellum,  the  massive  coordina- 
tion center  dorsally  of  the  up- 
per end  of  the  Medulla  ob- 
longata,   118,    119,    120,    122, 
127-130,    131,   155,   166,   172, 
204-215,  293 
cortex  of.     See  Cortex,  cerebellar 
development  of,  126,  127,  206 
fiber  tracts  of ,  141,  149,  173,  194, 

205,  206 
functions  of,  204,  267,  209-215, 

321,  339 
lesions  of,  207 
Cerebration,  unconscious,  331,  343 
Cerebrum,    that    portion    of    the 
brain  lying  above  the  Isthmus; 
also  used  as  synonymous  with 
Prosencephalon     and     Cerebral 
hemispheres,      130,     132,     155, 
175 
Chain,   sympathetic.     See   Trunk, 

sympathetic 
Chemical  processes  in  nerve-cells, 
102,  103,  105 
sensibility,  76,  91,  96,  97 
Chemotaxis,  111 

Chiasma,  optic  (chiasma  opticum), 
the  partial  decussation  of  the  op- 


INDEX    AND    GLOSSARY 


359 


tic  Tracts  on  the  ventral  surface 
of  the  brain,  127,  128,  129,  232, 
233   234 

Child,  C.  M.,  18,  32,  38,  103,  113 

Chimpanzee,  cerebral  cortex  of, 
315,  316 

Chorda  tympani,  160,  272 

Chorioid  plexus  (choioid  plexus). 
Sec  Plexus,  chorioid 

Chrionomus  plumosus,  nervous 
system  of,  31 

Chromatin,  a  nucleo-protein  sub- 
stance found  in  the  cell  nucleus, 
105 

Chromatolysis,  the  solution  and 
disappearance  of  the  chrome - 
philic  Substance  from  a  neuron, 
50,  51,  148,  316 

Chromophilic  bodies,  granules,  or 
substance.  See  Substance,  chro- 
mophilic 

Ciliarjf  process.  See  Process,  cili- 
ary 

Cingulum,  an  association  tract  of 
the  cerebral  hemisphere  lying 
under  the  Gyrus  cinguli,  296 

Circle  of  Willis,  a  polygonal  circuit 
of  anastomosing  arteries  on  the 
ventral  surface  of  the  brain,  from 
which  some  of  the  arteries  of  the 
brain  arise 

Circuit,  organic.     See  Reflex  circuit 

Circulation  of  the  blood,  apparatus 
of.  See  also  Vasomotor  appa- 
ratus, 95,  257,  261-263 

Cistern  (cisterna),  133 

Clarke,  column  of,  or  dorsal  nu- 
cleus of.  See  Nucleus,  dorsal,  of 
Clarke 

Claudius,  cells  of,  221 

Claustrum,  a  tliin  band  of  gray 
matter  l)et\veen  the  external 
Capsule  and  the  cortex  of  the 
island  of  Reil,  or  Insula 

Clava,  an  eminence  on  the  dorsal 
surface  of  the  lower  end  of  the 
medulla  oblongata  produced  by 
the  nucleus  of  the  Fasciculus 
gracilis,  141,  194,  205 

Cochlea,  the  Iwny  spirallj'  wound 
canal  containing  the  auditory 
receptor,  92,  218,  219,  222, 
224 

Co-consciousness,  330 


Coelenterates,  nervous  system  of, 

28,  252 
CoGHiLL,   G.  E.,   71,   73,  91,    100, 

146,  154,  199 
Cold,  sensations  of.     See  Tempera- 
ture, apparatus  of 
Cole,  L.  J.,  237 
Colic,  278 
Collateral,  a  small  side  branch  of  an 

Axon,  41,  45 
CoUiculus  facialis  (eminentia  facia- 
lis, eminentia  abducentis,  em- 
inentia teres,  Eminentia  medi- 
alis),  an  eminence  in  the  floor 
of  the  fourth  ventricle  pro- 
duced by  the  VI  nucleus  and 
the  Genu  of  the  facial  nerve, 
168 

inferior,  one  of  the  lower  pair  of 
Corpora  quadrigemina,  con- 
taining chiefly  reflex  auditorv 
centers,  123,  168,  171,  175; 
178,  191,  194,  203,  224,  225 

superior  (optic  lobe,  optic  tec- 
tum, nates),  one  of  the  upper 
pair  of  Corpora  quadrigemina, 
containing  chiefly  reflex  optic 
centers,  65,  66,  il9,  120,  123, 
164,  168,  175,  176,  178,  203, 
232,  234,  235,  293 
Collins,  .7.,  260 
Colon,  270 

Column,  anterior.     See  Funiculus 
V  entrails 

of  BuRDACH.  See  Fasciculus 
cuneatus 

of  Clarke.  See  Nucleus,  dorsal, 
of  Clarke 

dorsal  (colum.na  dorsalis  grisea. 
See  Column,  gray.  This  name 
is  also  applied  to  the  dorsal 
Funiculus^  137,  138,  139,  140, 
141,  144,  164,  165,  195 

of  Fornix.     See  Fornix  column 

fundamental.  See  Fasciculus 
proprius 

of  GoLL.     See  Fasciculus  gracilis 

gray  (columna  grisea),  one  of  the 
longitudinal  columns  of  neur- 
ones which  make  up  the  gray 
matter  of  tlie  spinal  cord. 
There  are  three  columns:  (1) 
dorsal  (posterior),  (2)  ventral 
(anterior),     and      (3)     lateral 


360 


INDEX   AND    GLOSSARY 


(middle  or  intermediate). 
These  columns  were  formerly 
called  horns  (cornua) ;  cf .  also 
Funiculus,  137,  138,  139,  140, 

164,  165 
intermedio-lateral,    of    spinal 

cord,  137,  158,  256 
lateral  (columna  lateralis  grisea ; 
see  Column,  gray),   139,   164, 

165,  256 

of  medulla  oblongata,  165-169 
posterior.    See  Funiculus,  dorsal 
somatic  motor,  164-169 

sensory,  164-169 
of  TtJRCK,  the  ventral  cortico- 
spinal Tract 
ventral     (columna    v  e  n  t  r  a  1  i  s 
grisea ;  see  Column,  gray.    This 
term  is  also  applied  to  the  ven- 
tral Funiculus),  137,  138,  139, 
140,  141,  164,  165 
vesicular.     See  Nucleus,  dorsal, 

of  Clarke 
visceral  motor,  164-169 
sensory,  164-169 
Columna.     See  Column 
Coma,  331 
Comma  tract  of  Schultze.     See 

Fasciculus  interfascicularis 
Coixmiissure  (commissura),  a  band 
of    fibers    connecting     corre- 
sponding parts  of  the  central 
nervous    system    across    the 
median  plane;  many  decussa- 
tions are  also  called  commis- 
sures, 294 
anterior   (.commissura  anterior), 
fibers   passing   transversely 
through  the  Lamina  terminalis 
and  connecting  the  basal  por- 
tions of  the  two  cerebral  hemi- 
spheres, 123, 177, 180, 244,  294 
dorsal,    fibers   which    cross   the 
midplane  of   the  spinal    cord 
dorsally  of  the  ventricle,  138 
of  fornix.     See   Commisstxre  of 

hippocampus 
of  GuDDEN.     See   Commissure, 

postoptic 
habenular  (superior  commis- 
sure), a  band  of  fibers  connect- 
ing the  two  Habenulae  im- 
mediately in  front  of  the  pineal 
Body,  294 


Commissure  of  hippocampus  (com- 
missura hippocampi,  commis- 
sura fornicis),  fibers  connect- 
ing the  Hippocampi  of  the  two 
sides  through  the  Fornix  body, 
184,  244,  294 
inferior.  See  Commissure,  post- 
optic 
of  Meynert.     See  Commissure, 

postoptic 
middle.     See  Massa  intermedia 
mollis.     See  Massa  intermedia 
posterior  (commissura  posterior), 
fibers     passing      transversely 
through  the  anterior  end  of  the 
roof  of  the  midbrain,  177,  244 
postoptic   (inferior  commissure), 
fibers     passing      transversely 
across  the  floor  of  the  hypo- 
thalamus associated  with  the 
optic    chiasma;   contains   the 
commissures  of  Gudden,  Mey- 
nert, and  other  fibers,  294 
soft.     See  Massa  intermedia 
superior.     See    Commissure, 

habenular 
of    tectum    (commissura    tecti), 
fibers     passing      transversely 
across  the   roof   of   the  mid- 
brain,    continuing    backward 
the  Commissura  posterior,  176 
ventral,   fibers  which   cross  the 
midplane  of  the  nervous  sys- 
tem ventrally  of  the  ventricle, 
138,  140,  144,  294 
Compensation  of  function  in  cor- 
tex, 328 
Components  of  nerves.     See  Sys- 
tem, functional 
Conarium.     See  Body,  pineal 
Conduct,  neurological  basis  of,  290, 

346-351 
Conduction,  avalanche,  the  sum- 
mation of  nervous  impulses  in 
a  center  so  as  to  increase  the 
intensitv   of    discharge,     107, 
214 
nervous,  39,  57,  102-107 
Cones  of  retina,  229-232,  235 
Conflict  in  evolution,  349 
Conjunctiva,  89,  90,  278 
Consciousness,  mechanism  of,  346 
dissociation  of,  330 
evolution  of.    See  Psychogenesis 


INDEX    AND    GLOSSARY 


3G1 


Consciousness,  of   lower  animals; 
of.  Psychogenesis,  33,  285, 339 
multiple,  330 
neurological  mechanism  of,  110, 
182,  249,  269,   277,    286-289, 
311-351 
seat  of,  325 
of  self,  349 
Continuity  of  consciousness,  331 
Convolution.     See  Gyrus 
of  Broca.     See  Broca's  convolu- 
tion 
Coordination,  the  combination  of 
nervous  impulses  in  juotor  cen- 
"  ters  to  ensure  the  cooperation  of 
the  appropriate  muscles  in  a  re- 
.  action,  36,  71,  198 
Cornea,  91,  277 
Cornu.     See  Horn 
Corona  radiata,  the  Projection  fib- 
ers which  radiate  from  the  in- 
ternal Capsule  into  the  cerebral 
hemisphere,  181,  184,  185,  296, 
321 
Corpora  quadrigemina,  the  dorsal 
part  of  the  Mesencephalon,  con- 
taining the  superior  and  inferior 
CoUiculi,  127,  128,  130,  175,  177, 
224,  234 
Corpus  callosum,  a  large  band  of 
commissural  fibers  connecting 
the  Neopallium  of  the  two  cere- 
bral   hemispheres,     128,    177, 
180,  181,  184,  244,  294,  296 
candicans.     See  Body,  mammil- 

lary 
dentatum.    See  Nucleus,  dentate 
fornicis.     See  Fornix  body 
geniculatum.     See  Body,  genicu- 
late 
mamillarc!.     See  Body,  mammil- 

lary 
I)ineale.     See  Body,  pineal 
ponto-bulbare,  123 
quadrigeminum.     See    Corpora 

quadrigemina 
restiforme  (restiform  body),  the 
inferior  peduncle  of  the  cere- 
bellum; cf.  Peduncle,  cerebel- 
lar, 142,  169,  170,  173,  194, 
205,  206,  214,  224 
striatum  (striate  body),  a  sub- 
cortical or  basal  nuiss  of  gray 
and  white  matter  in  each  cere- 


bral hemisphere,  123, 126, 127, 
132,   177,  180,  181,  183,    184, 
185,  190,  194,  239,  293,  321 
trapezoideum.     See  Body,  trape- 
zoid 
Correlation,    the    combination    of 
nervous  impulses  in  sensory  cen- 
ters resulting  in  adaptive  reac- 
tions, 36,  39,  44,  71,  114,  198,  346 
Correlation  neurone,  65,  144,  145 
Cortex,  cerebellar,  the  superficial 
gray  matter  of  the  cerebel- 
lum, 53,  54,  212,  213-215 
compared   with   cerebral  cor- 
tex, 204,  207,  214,  323,  339, 
342 
localization    of    function    in, 

207-210,  339 
neurones  of,  53,  54,  212 
cerebral  (pallium,  mantle),  asso- 
ciation   tissue   forming    the 
superficial    gray   matter   of 
the  cerebral  hemisphere,  27, 
69,    71,    79,    117,    125-130, 
132,  152,  182,  295-351 
areas  of.     See  Area,  cortical 
centers  of.     See  Center,  corti- 
cal 
dependencies  of,  122,  236 
development  of,  125-128,  320- 

324 
electric  excitability  of,  314 
evolution  of.     See  also  Hemi- 
spheres, cerebral,  compara- 
tive anatomy  and  evolution 
of,  122,  124,  292,  335 
functions   of,    110,    124,    131, 
204,  208,  214,  282,  311-351 
layers  of.     See  Layers  of  cere- 
bral cortex 
lesions  of,  282,  311-318,  325- 

328     _ 
localization     of    function     in. 
See  Localization  of  function 
in  cerebral  cortex,  and  Cen- 
ter, cortical 
motor  centers  of.     See  Center, 

cortical,  motor 
neurones  of,  43,  45,  298-308, 

323 
numlier  of  neurons  in,  27 
phylogeny     of.     See     Cortex, 

cerebral,  evolution  of 
structure  of,  292-309 


362 


INDEX   AND    GLOSSARY 


Cortex,  somatic.     See  Neopallium 

CoRTi,  cells  of  (hair  cells),  219-221 
ganglion    of.     See    Ganglion, 
spiral  organ  of.     See   Organ, 
spiral 
rod  of,  219,  221 
tunnel  of,  219,  221 

Cough,  mechanism  of,  266,  267 

CowDRY,  E.  v.,  49,  58 

Crista  ampuUaris,  218 
basilaris  of  cochlea,  219 

Crosby,  Elizabeth,  13,  120,  134, 
187 

Crozier,  W.  J.,  91,  100 

Crus,  a  stalk  or  peduncle,  applied 
to   compact   masses  of  fibers 
which  connect  different  parts 
of  the  brain;  cf.  Peduncle 
commune,  of  internal  ear,  218 
floccuU,  123 

fornicis.     See  Fornix,  crus  of 
olfactoria,  the  stalk  or  peduncle 
of  the  Olfactory  bulb 

Crusta.     See  Basis  pedunculi 

Crustaceans,  nervous  system  of,  30 

Culnien  monticuli,  210,  211 

Cuneus,  a  wedge-shaped  gyrus  on 
the  medial  face  of  the  posterior 
pole  of  the  cerebral  hemisphere 
receiving  visual  projection  fibers, 
128,  185,  234 

Cunningham,  D.  J.,  14 

Cup,  optic.  See  also  Vesicle,  op- 
tic, 228 

Curiosity,  348 

Current,  action,  102 

CusHiNG,  H.,  272,  273,  275,  319,  333 

Cyon,  nerve  of,  262 

Cytoplasm,  all  protoplasm  of  a  cell 
exclusive  of  that  in  the  nucleus, 
40,  102,  105,  108 

Davies,  H.  M.,  90,  101,  189 
Dearborn,  G.  V.  N.,  291,  345 
Diclive  monticuh,  210,  211 
Decussation   (decussatio),  a  band 
of  fibers  crossing  the  median 
plane  of  the  central  nervous 
system  and  connecting  unlike 
centers  of  the  two  sides;  many 
decussations  are  called   com- 
missxires 
of  FoREL.     See  Decussation,  teg- 
mental, ventral 


Decussation,   fountain.      See   De- 
cussation, tegmental,  dorsal 
of  Meynert.     See  Decussation, 

tegmental,  dorsal 
optic.     See  Chiasma,  optic 
of  pyramids,  142 
tegmental,    dorsal    (Meynert's 
decussation,  fountain  decus- 
sation), 143,  176 
ventral  (Forel's  decussation), 
142,  176 
Degeneration   of   nervous   tissues, 
46,  50,  51,  57,  146,  147,  316,  323 
Degeneration,  reaction  of,  317 

sclerotic,  of  cortex,  316 
Deiters,  cells  of,  in  spiral  Organ, 
219,  221 
vestibular  nucleus  of,  202,  203' 
Dejerine,  J.  J.,  321 
Dementia,  323 

Dendrite,  a  process  of  a  Neuron 
which  conducts  toward  the  cell 
body,  40,  41,  42,  43,  45,  47,  102, 
108,  110,  112 
Dependency,  cortical,  a  part  of  the 
brain  stem  developed  as  a  sub- 
sidiarv  of  the  cerebral  cortex, 
122,  208,  236,  339 
Depression,  108 

Development  of  the  nervous  sys- 
tem. See  Nervous  system,  de- 
velopment of 
Dewey,  J.,  21,  64,  72,  342,  343,  345 
DeWitt,  Lydia  M.  a.,  95,  99,  100 
Diaphragm,   innervation  of,   263- 

268 
Diaschisis,  a  transitory  defect  of 
function  due  to  disturbance  of 
cortical  equilibrium,  327 
Diencephalon  (betweenbrain,  thal- 
amencephalon),  the  brain  re- 
gion   lying    between    Mesen- 
cephalon and  Telencephalon; 
sometimes  called  Thalamus  or 
Optic  thalamus,  but  properly 
divided  into   Thalamus,  Epi- 
thalamus,  and  Hypothalamus, 
125-128,  130,  131,  176-183 
development  of,  125-128 
Diffusion  of  nerve  impulses,   111, 

214 
Digestion,  apparatus  of,   83,  249, 

257,  268-270,  283 
Dilemma,  62,  341 


INDEX    AND    GLOSSARY 


363 


Dioptric  iipptirtitus  of  cyelxill,  229 

J)isagreeable  and  agreeable.  Sec 
Aitection 

Discrimination.  See  Reaction,  dis- 
criminative 

Dissociation  of  consciousness,  330 

Distention,  sensations  of,  95 

DOCKERAY,  F.  C,  113 

Dog,  functions  of  cortex  of,  312, 
314,  320 
scratch  reflex  of,  146 

Dogfish,  nervous  system  of.  See 
Fishes,  nervous  system  of 

DoGiEL,  A.  S.,  88,  89,  90,  254,  259 

DoLLEY,  D.  H.,  44,  58,  108,  109, 
113 

Dolphin,  absence  of  olfactory  or- 
gans of,  240 

Donaldson,  H.  H.,  113,  133,  134 

Dorsal,  on  the  back  side  of  the 
body,  termed  posterior  in  the 
B.  N.  A.  hsts,  125 

Ductus  cochlearis,  217-219 
endolymphaticus,  217,  218 
reuniens,  218 

semicircularis.     See  Canal,  semi- 
circular,  and    Vestibular   ap- 
paratus 
utriculo-saccularis,  218 

Dura  mater,  the  outer  brain  mem- 
brane, 133 

DuRUPT,  A.,  209,  216 

Dvnamic  theory  of  consciousness, 
327,  330 


Ear.     See  Auditory  apparatus  and 
Vestibular  apparatus 
brain,  121,  133 
evolution  of,  223 

Earthworm,  nervous  sj'stem  of,  29 

Eastman,  Max,  286 

Ectoderm  (epiblast),  the  outer 
germ  layer  of  the  embryo,  from 
which  the  epidermis  and  the 
Neural  tube  develop,  228 

Edgeworth,  F.  H.,  197 

Edinger,  L.,  38,  124,  134,  174,  244, 
248,  312,  333,  340 

Edinger-Westphal,  nucleus  of 
(the  visceral  efferent  nucleus  of 
the  III  nerve;  cf.  Nucleus  of 
oculomotor  nerve) 

Education,  33,  .346-351 


Effector,  an  organ  of  response,  27, 
98 

Efferent,  conducting  away  from  a 
center,  27,  44,  116,  137,  148 

Electric  excitability  of  nervous  tis- 
sues, 314,  316,  319 
phenomena    in    nervous    tissue, 
102 

Embryology  of  nervous  system. 
See  Nervous  system,  embryology 
of 

Eminentia   abducentis.     See    Col- 
liculus  facialis 
facialis.     See  Colliculus  facialis 
hypoglossi.    See  Trigonum  hypo- 

glossi 
medialis  (eminentia  teres),  a 
medial  longitudinal  ridge  in 
the  floor  of  the  fourth  ventri- 
cle; an  enlarged  portion  is  the 
Colliculus  facialis 

Eminentia   teres.     See   Eminentia 
medialis 
vagi.     See  Ala  cinerea 

Emotion.     See  Affection 

Empis  stercorea,  nervous  svstem 
of,  31 

Encephalon,  the  brain,  129 

End-nucleus.  See  Nucleus,  ter- 
minal 

Endolymph,  218 

End-organ,  the  peripheral  appar- 
atus related  to  a  nerve;  a  Recep- 
tor or  Effector,  26,  74,  84-99 

End-plate,  motor;  the  terminal  ar- 
borization of  a  motor  axon  upon 
a  muscle-fiber,  41,  98,  108 

Endyma.     See  Ependyma 

Engram,  329 

Environment,  17,  18,  74,  347 

Epencephalon,  the  cerebellum 

Ependyma  (endyma),  the  lining 
membrane  of  the  ventricles  of 
the  brain,  derived  from  the  orig- 
inal epithelium  of  the  Neural 
tube,  39 

Epiblast.     See  Ectoderm 

Epicritic  sensibility,  a  highly  re- 
fined type  of  cutaneous  sensi- 
bility, especially  on  hairless 
parts,  89,  90 

Epiglottis,  organs  of  taste  upon, 
161,  272 

Epinephrin.     See  Adrenalin 


364 


INDEX   AND    GLOSSARY 


Epiphysis.     See    Body,    pineal 

Epithalamus,  the  dorsal  subdi- 
vision of  the  Diencephalon,  con- 
taining the  pineal  Body  and  the 
Habenula,  an  inaportant  olfac- 
tory correlation  center,  119,  120, 
127,  128,  130,  131,  177,  178,. 180, 
182,  244,  245,  247 

Epithelium,  a  thin  sheet  of  cells,  25 
nerve  endings  in,  96 
olfactorjr     (Schneiderian     mem- 
brane), 97,  242 

Equilibrium,     apparatus    of.     See 
also  Vestibular  apparatus,  82, 
93,  94,  161,  201,  204,  222,  223 
nervous,  70,  327,  330 
theorv  of  consciousness,  330 

Esophagus,  83,  95,  156,  161,  261, 
270 

Esthetic  experience.     See  Affection 

Ethics.     See  Morals 

Eugenics,  346 

Eustachean  tube  (auditorv  tube), 
217 

Evolution  of  mind.     See  Psycho- 
genesis 
of  Nervous  sj^stem.     See  Nerv- 
ous sj'stem,  evolution  of 

EwALD,  J.  R.,  202,  226 

Excitability,  electric.  See  Electric 
excitability  of  nervous  tissues 

Excitation,  fatigue  of,  108,  109 

Experience,  learning  by,  35,  328, 
341,  342,  347,  350 

Exteroceptor,  a  sense  organ  excited 
by  stimuli  arising  outside  the 
body,  79,  82,  84 

Exteroceptors,  apparatus  of,  143, 
149,  150,  152,  159,  178-182,  189- 
192,  278 

Extirpation  of  cortical  centers,  311, 
312,  320 

Eycleshymer,  a.  C,  124,  134 

Eye.     See  Visual  apparatus 

accommodation  of.     See  Accom- 
modation of  vision 
brain  (ophthalmencephalon),  121, 

132 
conjugate    movements    of,    204, 

235,  314 
development  of,  125,  126,  228 
evolution  of,  236 
muscles  of,  98,  118, 155,  159,  160, 
197,  257,  274 


Eye,  parietal.     See  Parietal  eye 
pineal.     See  Parietal  eye 


Face  brain,  132 

Faculties,   mental,    313,   319,   324, 

325 
Falx  cerebri,  a  longitudinal  fold  of 
Dura       mater       which    extends 
between  the  cerebral  hemispheres 
in  the  longitudinal  fissure,  133 
Fascia  dentata.     See  Gyrus  denta- 

tus 
Fasciculus,  a  bundle  of  nerve-fibers 
not  necessarily  of  similar  func- 
tional connections.     The  term 
is  often  used,   however,  as  a 
synonym  for  Tract,  139 
antero-lateralis    superficialis    (of 
GowERs).    See  Fasciculus  ven- 
tro-lateralis  superficialis 
cerebello -spinalis.     See       Tract, 

spino-cerebellar 
cerebro-spinalis.     See    Tract, 
cortico -spinal 
circumolivaris  pyramidis,  123 
communis,   a   name   formerly   ap- 
phed   to   the   Fasciculus   solita- 
rius  in  lower  vertebrate  brains 
cuneatus    (column    of    Burdach), 
the     lateral     portion     of    the 
dorsal  funiculus  of  the  spinal 
cord,   139,  141,   150,  193,  194 
nucleus     of.     See     Tuberculum 
cuneatum 
dorso-lateralis     (Lissatier's    zone, 
Lissauer's     tract),     141,     263, 
281 
of    GowERS.     See    Fascicul  us 

ventro-lateralis    superficialis 
gracilis     (column    of    Goll),    the 
medial  portion  pf  the   dorsal 
Funiculus  of  the  spinal  cord, 
139,  141,  150,  193,  194 
nucleus  of.     See  Clava 
interfascicularis      (comma      tract, 
tract   of  S  c  H  u  L  T  z  e),    141, 
143 
longitudinalis  inferior  of  cerebral 

hemisphere,  246,  296 
longitudinaUs      medialis      (medial 
longitudinal     bundle,     posterior 
longitudinal    bundle,    fasciculus 
longitudinalis  posterior  or  dor- 


INDEX   AND    GLOSSARY 


365 


salis),  a  bundle  of  motor  co- 
ordination libers  runuiiifi; 
through  tlie  brain  stem,  143, 
166,  169,  170,  176,  194,  199, 
203,  224,  235 

longitudinahs  superior  of  cere- 
bral hemisphere,  296 

marginalis  ventralis,  143 

of  Meynert.  See  Tract,  haben- 
ulo-peduncular 

occipito-frontalis  inferior  of  cere- 
bral hemisphere,  296 

proprius  of  cerebral  hemisphere. 
See  Fibers,  arcuate  (1) 

proprius  of  spinal  cord  (funda- 
mental columns,  basis  bundles, 
ground  bundles),  that  portion 
of  the  white  matter  of  the 
spinal  cord  which  borders  the 
gray  matter  and  contains  cor- 
relation fibers;  arranged  in 
dorsal,  lateral,  and  ventral 
subdivisions,  138,  141,  143, 
144,  197,  199,  279,  280, 
287 

retroflexus  of  Meynert.  See 
Tract,  habenulo-peduncular 

solitarius  (tractus  solitarius,  soli- 
tary bundle,  in  lower  verte- 
brates often  called  Fasciculus 
com  munis),  a  longitudinal 
bundle  of  fibers  in  the  medulla 
oblongata  containing  the  cen- 
tral courses  of  the  visceral  sen- 
sory root-fibers  of  the  cranial 
nerves,  163, 164,  169,  170,  178, 
261,264 

sulco-marginalis,  141,  143 

thalamo-mamillaris.  See  Tract, 
mamillo-thalamic 

transversus  occipitalis  of  cerebral 
hemisphere,  296 

uuciuatusof  cerebral  hemisphere, 
296 

ventro-lateralis  superticialis  (an- 
tero-lateral   fasciculus,    Gow- 
ERS'  tract),  139,  142 
Fatigue,  107-109,  283,  286,  338 
Fear.     See  also  Affection,  95,  283, 

284 
Feeble-mindedness.     See  Idiocy 
Feeding,  reflexes  of.     Sec  Reflexes 

of  feeding 
Feeling  (affective).     See  Affection 


Feeling  tone.     See  also  Affection, 

277,  282,  286-289 
Ferrier,  D.,  216 

Fiber,  or  fibers,  fibrae.     See  Nerve - 
fiber 
arcuate,  of  the  cerebral  hemi- 
sphere,    short     association 
fibers  connecting  neighbor- 
ing gyri;   also   called  fibrae 
propria    and  fasciculi   pro- 
prii,  296,  319 
of  the  medulla  oblongata,  de- 
cussating fibers  lying  in  a 
superficial    series    (external 
arcuate  fibers)  and  a  deep  se- 
ries (internal  arcuate  fibers), 
169 
association;   cf.    Tract,    associa- 
tion, 296,  303,  319,  325-327 
of  MtJLLER,  229,  230 
postganglionic.     See   Neuron, 

postganglionic 
preganglionic.    See  Neuron,  pre- 
ganglionic 
projection.    See  Proj  action  fibers 
propriaj    (arcuate   fibers   of   the 
cerebral  hemisphere),  296,  319 
Field,  auditory  psychic,  319 

cortical,  a  term  sometimes  used 
as  a  synonym  of  Center,  corti- 
cal, or  of  Area,  cortical 
visual  psychic,  319 
Fila    olfactoria,    the    filaments    of 
which  the  olfactory  nerve  is  com- 
posed, 97,  160,  242 
Fillet.     See  Lemniscus 
Filum    terminale     (terminal    fila- 
ment), the  slender  caudal  termi- 
nation of  the  spinal  cord,  115 
Fimbria,   a  band  of  fibers   which 
borders   the    Hippocampus   and 
joins  the  Fornix,  180,  244,  246, 
294 
Final  common  path,  61,  65,  107, 

286 
Fischer,  B.,  312,  333 
Fishes,    nervous    sj'stem    of,    117, 
118-120,  132,  163-167,  181,  197, 
199,  205,  222,  223,  236,  239,  264, 
268,  273,  311,  337 
Fiske,  E.  W.,  13 

Fissure  (fissura),  in  the  cerebral 
cortex  a  deep  fold  whicii  in- 
volves the  entire  thickness  of 


366 


INDEX   AND    GLOSSARY 


the    brain    wall;    cf.    Sulcus. 
This  is  the  usage  of  the  B.  N. 
A.,  but  fissure  and  sulcus  are 
often  used  as  synonyms  and 
the  B.  N.  A.  is  not  consistent 
in  this  matter 
Fissure,  calcarine,  128 
chorioid,  the  fold  in  the  postero- 
medial   wall   of  the    cerebral 
hemisphere  through  which  the 
lateral     chorioid     Plexus      is 
invaginated 
dorsal,    of    spinal    cord    (dorsal 

median  septum),  139,  140 
ectorhinal.     See  Fovea  limbica 
hippocampal,  246 
lateral   (fissura  laterahs  Sylvii, 
fissure  of  Sylvius),  a  deep  fis- 
sure on  the  lateral  surface  of 
the  cerebral  hemisphere  which 
separates  the  temporal  from 
the  frontal  and  parietal  lobes, 
130,  181,  295 
longitudinal,   the    great    fissure 
between     the     two     cerebral 
hemispheres,  129,  294 
parieto-occipital,    128,    130,  185 
prima    (sulcus   primarius),    209, 

210,  211 
rhinal.     See  Fovea  limbica 
of   Rolando.     See    Sulcus   cen- 
tralis 
secunda,  210,  211 
ventral,  of  spinal  cord,  138,  139, 
140 
Fistula,  gastric,  269 
Flatau,  Ed.,  14 
Flechsig,  p.,  320-322,  333,  334 
tract  of.     See  Tract,  spino-cere- 
bellar,  dorsal 
Flexure,  a  bending  or  crumpling  of 
the     developing     Neural     tube 
caused  by  unequal  growth  of  its 
parts,  as  cervical,  pontile,  mesen- 
cephalic, diencephahc,  and  telen- 
cephalic  flexures,  125-128 
Flies,  nervous  system  of,  31 
Flocculus,  the  most  lateral  lobe  of 

the  cerebellum,  209,  210 
Flourens,  J.  P.  M.,  266 
Fluid,  cerebro-spinal,  a  clear  liquid 
filling  the  ventricles  of  the  brain 
and  spinal  cord   and  subarach- 
noid space,  133 


Folium,  one  of  the  leaf -like  subdivi- 
sions of  the  cerebellar  cortex; 
these  are  termed  Gyri  in  the 
B.  N.  A.,  212 

vermis,  211 
Foramen  interventriculare  (fora- 
men of  Monro,  porta),  the 
communication  between  the 
lateral  and  the  third  ventri- 
cles, 177,  293 

of  Magendie,  an  aperature  in  the 
membranous  roof  of  the  fourth 
Ventricle 

of  Monro.     See  Foramen  inter- 
ventriculare 
Forebrain.     See  Prosencephalon 
FoREL,    decussation   of.     See    De- 
cussation, tegmental,  ventral 

field  of,  183 
Formatio  bulbaris  (bulbar  forma- 
tion), the  tissue  comprising 
the  primary  olfactory  center 
in  the  olfactory  bulb,  i.  e.,  the 
Glomeruli,  mitral  Cells,  and 
granule  Cells,  244 

reticularis  (reticular  formation, 
processus  reticularis  in  spinal 
cord),  a  mixture  of  nerve- 
fibers  and  cell  bodies  providing 
for  local  reflexes,  69,  138,  140, 
167,  170,  171,  172,  191,  194, 
198,  202,  266,  274,  338,  345 

vermicularis,  209 
Fornix,  a  complex  fiber  system  con- 
necting the  Hippocampus  with 
other  parts  of  the  brain,  177, 
178,  180,  181,  246 

body  (corpus  fornicis),  the  mid- 
dle part  of  the  Fornix 

columns  (columnae  fornicis,  an- 
terior pillars  of  fornix),  two 
columnar  masses  of  fibers  di- 
verging from  the  anterior  end 
of  the  Fornix  body  to  descend 
into  the  diencephalon,  180, 
185,  244,  247 

commissure.  See  Commissure 
of  hippocampus 

crus  of  (crus  fornicis,  posterior 
pillar  of  fornixj,  a  band  of 
fibers  on  each  side  of  the  bi-ain 
connecting  the  posterior  part 
of  the  Fornix  body  with  the 
Fimbria 


INDEX    AND    GLOSSARY 


367 


Fornix,    longus    of    Fouki.,    IUxms 
which  pcrt'orato  the  Corpus   cal- 
losum    and     pass    thvoutih     liic 
Septum  pellucidum 
Fossa  lateralis  (fossa  of  .Sylvius), 
a  deepei-  part  of  the  Fissura 
lateralis  containing  the  Insula 
rhomboidal,    the    floor    of    the 
fourtli  ventricle,  127 
Fovea  limbica  (sulcus  rhinalis,  fis- 
sura rhinica,  fissura  rhinalis,  fis- 
sura   eetorhinalis),    the      sulcus 
which  uuxrks  the  lateral  border 
of  the  lateral  Area  olfactoria  and 
Gyrus   hippocampi   or   pyriform 
Lobe  in  the  lower  mammals 
Franz,  S.  I.,  334 
Freedom  of  action,  349 
Frey,  M.  von,  90,  100 
Fritsch,  G.,  314,  334 
Frog,  cerebral  cortex  of,  240,  293, 
311 
nerve  endings  in,  96 
reaction  time  of,  104 
reactions  of,  66 

velocity  of  nervous  transmission 
in,  103 
Funiculus,  one  of  the  three  princi- 
pal divisions  of  white  matter 
on  each  side  of  the  spinal  cord ; 
these   funiculi   were   formerly 
called  Columns,  139 
dorsal  (funiculus  dorsalis  or  pos- 
terior, posterior  columns),  the 
white  matter  of  the  spinal  cord 
included    between    the  dorsal 
fissure    and    the    dorsal    root, 
139,  141,   149,  150,  152,  164, 
165,  193,  194,  195-198,  345 
lateral  (funicuhis  lateralis,  later- 
al columns),  the  white  matter 
of    the   spinal   cord   included 
between  the  dorsal  and  ventral 
roots,  139 
ventral    (funiculus   ventralis   or 
anterior,  ventral,  or  anterior 
.columns),  the  white  matter  of 
the  spinal  cord  included  be- 
tween the  ventral  fissure  and 
the  ventral  root,  139 

Gall,  F.  G.,  312,  313,  334 

Galvanotaxis,  112 

Ganglion,  a  collection  of  nerve-cells. 


Ill  vertebrates  the  term  shoulil 
l)e  applied  only  to  peripheral  cell 
masses,   though  sometimes  Nu- 
clei within  the  brain  are  so  desig- 
nated, 116,  117 
Ganglion  or  ganglia,  basal,  a  term 
sometimes  applied  to  the  Cor- 
pus  striatum  and  other   siib- 
cortical  parts  of  the  cerebral 
hemisphere 
branchial,  of  vagus,  163 
cerebro-spinal,   development  of, 

49 
cervical,  inferior,  251 
middle,  251 
superior,  251,  261 
ciharv,  155,  160,  163,  251,  256, 

274 
of  CoRTi.     See  Ganghon,  spiral 
of  facial  nerve.     See  Ganglion, 

geniculate 
Gasser's.     See  Ganglion,  semi- 
lunar 
geniculate  (ganglion  geniculi,  the 
ganglion  of  the  VII  cranial  or 
facial  nerve),    119,    120,    160, 
163,  272,  273 
habenulce.         See  Habenula 
of  insects,  30,  31 
interpedunculare.     See  Nucleus, 

interpeduncular 
of  invertebrates,  29,  30,  31,  252 
jugular  (ganglion  jiigulare),  161, 

163 
of  lateral  Hne  nerves,  163,  223 
nodosum,  161,  264,  267 
opticum    basale.     See    Nucleus, 

preoptic 
otic,  161,  272 
petrosal     (ganglion     petrosuni), 

161,  272 
of  Scarpa.    See  Ganglion  vestib- 
ular 
semilunar  (ganglion  semihmare, 
Gasser's  ganglion,    the   gan- 
glion of  the  V  cranial  or  tri- 
geminal nerve),  46,  119,  120, 
160,  197,  272 
sphenopalatine,  251,  272 
spinal,  26,  46,  116,  136,  137,  145, 

146,  147,  152,  161,  253,  254 
spiral  (ganglion  spirale,  ganglion 
of  CoRTi),  161 

submaxillary,  160 


368 


INDEX   AND    GLOSSARY 


Ganglion,  superior  (ganglion  supe- 
rius  of  IX cranial  nerve),  161 
supra-esophageal,  29,  30 
sympathetic,  56,  115,  117,  136, 
137,  250,  251,  252-258 
prevertebral,  sympathetic  gan- 
glia of  the  thorax  and  abdo- 
men other  than  those  of  the 
sympathetic  trunk 
vertebral,  the  ganglia  of  the 
sympathetic  Trunk 
terminale,  239 
of    trigeminus.     See     Ganglion, 

semilunar 
of  vagus.     See  Ganglion,  jugular, 

and  Ganglion  nodosum 
of  vertebrates,  116 
vestibular  (ganglion  of  Scarpa), 
161 
Gaskell,  W.  H.,  158,  174 
Gehuchten,  a.  van,  14,  26,  46,  91, 

216 
Generative     organs.     See     Sexual 

organs 
Geniculate  body.     See  Body,  gen- 
iculate 
ganglion.     See  Ganglion,  genicu- 
late 
Gennari,  layer   of  stripe  of.    See 

Line  of  Gennari 
Genu,  a  knee- shaped  bend  of  an 
organ,  such  as  the  genu  of  the 
corpus  callosum,  of  the  facial 
nerve,  etc. 
of  corpus  callosum,  128 
Gills,  263,  268 

innervation   of,    118,    119,    121, 

163,  273 
muscles  of,  99,  162 
Gland,  adrenal.     See  Gland,  supra- 
renal 
intestinal,  249 
nerve-endings  on,  98 
pineal.     See  Body,  pineal 
pituitary.     See  Hypophysis 
salivary,     innervation    of,     156, 
160, 161, 168, 170, 257, 269,  271 
suprarenal,  258,  283,  284 
Glia.     See  Neuroglia 
Glomeruli,  olfactory,  small  globu- 
lar masses  of  dense  Neuropil  in 
the  olfactory  bulb  containing  the 
first    synapse    in    the    olfactory 
pathway,  242,  243 


Glycosuria,  283 
Goldstein,  K.,  142,  216 
GoLGi,  C.,  43,  45,  46,  51,  58 
GoLL,  column  of.     See  Fasciculus 

gracilis 
GoLTZ,  F.,  311,  313,  334 
GowERS,  fasciculus  of.     See  Fas- 
ciculus   ventro-lateralis   superfi- 
cialis 
Gradient,  physiological,  in  nerve- 
fibers,  103 
Granules.     See  Cells,  granule 
chromophilic,  tigroid,  of  Nissl. 
See  Substance,  chromophilic 
Gray,  central,  relatively  undifferen- 
tiated gray  Matter  ivhich  retains 
its  primitive  position  near  the 
ventricles,  138 
Groove,    medullary.     See    Neural 
groove 
neural.     See  Neural  groove 
GRtJNBAUM,  A.  S.  F.,  315,  334 
GuDDEN,  commissure  of.    See  Com- 
missure, postoptic 
Guild,  S.  R.,  240,  248 
GuLiCK,  Luther  H.,  13 
Gu^tatorv   apparatus,   77,   79,   96, 
156,  160,  161,  162,  164,  172,  179, 
242,  261,  270-274,  337 
Gyrus,  one  of  the  convolutions  ox 
folds   of   the    cerebral   cortex 
bounded  by  Sulci  or  Fissures, 
295 
angularis,  130  _ 

centralis  anterior  (precentral  gy- 
rus),-130,  151,  198,300,301, 
304,  305,  307,  315,  316,  317- 
320,  322 
posterior   (postcentral  gyrus), 
130,  299,  301,  304,  306,  315, 
316,  318-320,  322 
cinguh,  128,  184 
dentatus     (fascia     dentata),     a 
subsidiary  gyrus   of  the  Hip- 
pocampus, 246 
fornicatus  (limbic  lobe),  the  mar- 
ginal portion  of  the  cerebral 
cortex  on  the  medial  aspect  of 
the  hemisphere,  including  the 
Gyrus   cinguh,    Gyrus  hippo- 
campi, and  others;  there  is  a 
variety  of  usage  regarding  its 
limits 
frontalis  inferior,  130,  185,  326 


INDEX    AND    GLOSSARY 


:w.) 


Gyrus  frontalis,  iiicdius,  130 
superior,  128,  130 

hippocampi,  that  ])art()f  thecerc- 
bral  cortex  which  liordcrs  the 
Hippocampus.  Part  of  it  (the 
Uncus)  is  Archipallium ;  the  re- 
mainder is  transitional  to  the 
Neopallium.  See- Lobe,  pyri- 
form,  241,  243,  246,  306,  318 

lingualis,  128 

occipitalis  lateralis,  130 

olfactorius    lateralis.     See  Nu- 
cleus olfactorius  lateralis 
medialis.     See     Area     parol- 
factoria  of  Broca 

orbitalis,  130 

postcentral.  See  Gyrus  centralis 
posterior 

precentral.  See  Gyrus  centralis 
anterior 

subcallosus  (pedunculus corporis 
callosi),  part  of  the  Nucleus 
olfactorius  medialis,  128,  244 

supramarginalis,  130 

temporalis  inferior,  130 
medius,  130 
superior,  130,  185 

uncinatus.     See  Uncus 


Habenula  (nucleus  habenulse,  gan- 
glion habenulse),  an  important 
olfactory  correlation  center  in 
the  Epithalamus,  177,  180,  183, 
185,  244 

Habit,  physiological,  33,  328,  338 

Hair  cells  (cells  of  Corti),  219,  220, 
221 
innervation  of,  94 

Halliburton,  W.  D.,  133,  134 

Hardesty,  I.,  13,  39,  58,  220,  222, 
226 

Harris,  W.,  237 

Head,  H.,  88,  89,  100,  101,  154, 
182,  187,  189,  191,  192,  195,  196, 
259,  279,  281,  282,  291,  334,  346 

Hearing,  organs  of.  See  Auditory 
apparatus 

Heart,  innervation  of,  156,  161, 
257,  261 

Heat,  sensations  of.  See  'IVniper- 
ature,  apparatus  of 

Heidenhain,  M.,  52,  58 

Held,  H.,  52,  221,  226 
24 


Helmholtz,  it.  L.  T.  von,  220,  226 
Helwk;,     tract     of.     See     Tract, 

olivospinal 
Hemianopsia,  312 
Hemiplegia,  motor  paralysis  of  one 

side  of  the  body,  317 
Hemispheres,  cerebellar,  129,  20.S, 
210 
cerebral,  66,  67,  119,  120,  130, 
132,  140,  175,  239,  245,  293, 
294,  311 
comparative     anatoniv     and 
evolution  of,  119,  120,  122, 
140,  239,  293,  311,  312,  324, 
328,  33,5-340 
Hemorrhage,  cerebral,  327 
Hensen,  cells  of,  221 

stripe  of,  221 
Herrick,  C.  Judson,  13,  38,  64, 
71,  72,  73,  100,  120,  134,  146, 
154,  155,  172,  174,  182,  187,  199, 
205,  216,  223,  248,  275,  276,  293, 
337 
Herrick,  C.  L.,  17,  116,  216,  287, 

291,  330,  334,  337 
Herrick,  F.  H.,  64,  73 
Hertz,  A.  F.,  100,  270,  276 
Hess,  C.  L.  von,  263,  276 
Hibernation,  nerve  cells  in,  108 
Hindbrain,  a  term  which  has  been 
variously  applied  to  the  cerebel- 
lum,  the  cerebellum  and  pons, 
the  medulla  oblongata,  and  the 
entire  rhombencephalon 
Hippocampal    gyrus.     See    Gyrus 

hippocampi 
Hippocampus  (hippocampus major, 
Amnion's    horn,    cornu    Am- 
monis),    a    submerged    gyrus 
forming  the  larger  part  of  the 
Archipallium,  or  olfactorv  cere- 
bral   cortex,    241,    244,    246, 
247,  306,  318,  341 
commissure    of.     See    Commis- 
sure of  hippocampus 
minor.     See  Calcar  avis 
His,  William,  51,  58,  124-127,  134 
Histology,  the  studv  of  Tissues 
HiTZRi,  E.,  314,  334 
Hodoe,  C.  F.,  113 
Hofeu,  H.,  222,  226 
Holmes,    G.,    182,    187,   282,   291, 

312,  334,  346 
Holmes,  S.  J.,  291 


370 


INDEX    AND    GLOSSARY 


Horn  (cornu),  one  of  the  three  chief 
parts  of  the  lateral  ventricle — 
anterior,  posterior,  and  inferior 
or  middle;  also  applied  to  the 
gray  Columns  of  the  spinal  cord 
of  Ammon.    See  Hippocampus 

Hormone,  a  specific  chemical  sub- 
stance contained  in  an  internal 
secretion  and  carried  by  the 
blood  or  lymph  to  another  organ 
which  it  excites  to  functional 
activity,  111,  249 

Hough,  Th.,  73 

HuBER,  G.  C,  92,  93,  99,  100,  240, 
248,  259 

Humor,  vitreous,  229 

Hunger,  apparatus  of,  95,  268 

HuscHKE,  teeth  of,  221 

Hyodon  tergissus,  brain  of,  337 

Hypophysis  .(pituitary  body,  pitui- 
tary gland),  a  glandular  append- 
age to  the  ventral  part  of  the 
hypothalamus;  its  posterior  lobo 
is  an  outgrowth  from  the  Neural 
tube,  its  anterior  lobe  is  an  in- 
growth from  the  epithelium  of 
the  embryonic  mouth  cavity, 
123,  128,  178,  183 

Hypothalamus,  the  ventral  subdi- 
vision of  the  Diencephalon,  con- 
taining the  Hypophysis  and  the 
mammiUary  Body,  an  important 
olfactorj^  correlation  center,  126, 
127,  130.  131,  179,  180,  181,  183, 
191,  194,  240,  244,  245,  247,  274, 
288 


Idiocy,  311,  323 

Imbecility.     See  Idiocy 

Impulse,  nervous,  nature  of,  102, 
103 
velocity  of,  103,  104 

Infundibulum,  a  funnel-shaped  ex- 
tension of  the  third  ventricle 
passing  through  the  Hypothala- 
mus to  the  end  in  the  Hypophy- 
sis, 123,  128,  129,  178 

Inhibition,  the  diminution  or  arrest 
of  a  function,  66,  70,  116,  285, 
311,  341 

Insanity,  323 

Insects,  nervous  system  of,  30,  31 
respiration  of,  263 


Instinct,  a  complex  form  of  invari- 
able Behavior,  32,  64,  285,  292, 
323,  335,  341,  343,  346-348 

Insula  (island  of  Reil),  a  portion  of 
the  cerebral  cortex  which  is  sub- 
merged under  the  Fossa  lateralis, 
181,  184,  295,  306 

Integration,  the  combination  of 
different  acts  so  that  they 
cooperate  toward  a  common 
end,  25,  37,  114,  122 

Intelligence.     See  Consciousness 
lapsed,  33,  335,  343   , 

Interbrain.     See  Diencephalon 

Interference  of  nervovis  impulses, 
62,  64,  66,  341 

Internuncial  pathways,  correlation 
tracts  connecting  different  cen- 
ters or  nuclei  within  the  central 
nervous  system,  69 

Interoceptor,  a  sense  organ  excited 
by  stimuli  arising  within  the  vis- 
cera; cf.  Visceral  apparatus  and 
Visceral  organs,  79,  82,  93,  270 

Intestines,  nerves  of,  156,  261,  268, 
269 

Intoxication,  effects  of,  103,  108, 
109,  110,  256,  286 

Introspection,  104,  331,  343 

Intumescentia  cervicalis  (cervical 
enlargement),  the  enlargement 
of  the  spinal  cord  from  which 
the  nerves  of  the  arm  arise 
lumbalis  (lumbar  enlargement), 
the  enlargement  of  the  spinal 
cord  from  which  the  nerves  of 
the  leg  arise 

Invariable  behavior.  See  Behav- 
ior, invariable 

Invertebrates,  behavior  of,  31 
nervous  system  of,  29 

Iris,  155,  235,  257,  261,  274 

Irradiation  of  nervous  impulses,  69, 
70,  106,  289 

Island  of  Reil.     See  Insula 

Isthmus,  a  narrow  segment  of  the 
brain  forming  the  upper  end  of 
the  Rhombencephalon  (B.  N. 
A.);  it  might  better  be  regarded 
as  merely  the  plane  of  separation 
between  Rhombencephalon  and 
Cerebrum,  125-128,  130,  131, 
155,  175 

Iter  (iter  a  tertio  ad  quartum  ven- 


INDEX    AND    GLOSSARY 


:}7i 


triculum).     Sec  Aqueduct  of  Syl- 
vius 

Jackson,  Hughlings,  325 
Jacobson,   nerve  of.     Sec   Nerve, 
tympanic 
organ  of.     See  Organ,  voniero- 

James,  W.,  288,  291 

Jelly-fishes,  nervous  system  of,  28, 

252 
Jennings,  H.  S.,  21,  32,  38,  73 
Jewett,  Francis  Gulick,  13 
Johnston,  J.  B.,  14,  135,  159,  166, 

174,  187,  197,  248 
Joints,  nerve-endings  in,  93 

Kangaroo,  cerebral  cortex  of,  241 
Kappers,  C.  U.  Ariens,  112,  113, 

226,  248,  266,  276,  295,  310,  344 
Karplus,  J.  P.,  279,  291,  312,  334 
Karyoplasm,  the  protoplasm  of  the 

nucleus  of  a  cell,  102 
Keibel,  F.,  135 
Kolliker,  a.,  45 
Krause,  W.,  124,  135 

end-bulbs  of,  89,  90 
Kreidl,  a.,  279,  291,  312,  334 
Kries,  J.  VON,  76 
KuNTZ,  A.,  259 

Labium  vestibulare,  221 
Labyrinth  of  ear,  217,  218 
Lactic  acid,  109 
Ladd,  G.  T.,  104,  113,  238 
Lagena,  222,  223 
Lamina.     See  also  Layer 

affixa,  a  thin  non-nervous  part  of 
the  medial  wall  of  the  cerebral 
hemisphere    attached    to    the 
thalamus  and  bordered  by  the 
lateral  chorioid  Plexus, 
epithelialis,  133 
of  neural  tube.     See  Plate 
terminalis  (terminal  plate),  the 
anterior  boundarj^  of  the  third 
ventricle,  127,  180,  239,  293, 
294 
Lancisi    (Lancisius),    nerves    of. 
See  Stria  longitudinalis 
stria^  of.    See  Stria  longitudinalis 
Landacri:,  F.  L.,  36 
L.vnge,  C,  288,  291 


Langley,  J.  N.,  162,  2.52,  25S,  259, 

260 
Laqyeus.     See  Lemniscus 
Larynx,  267 
Lateral  line  organs.     See  Organs, 

lateral  line 
Law,  Bell's,  158 

myelogenetic,  of  Flechsig,  320 
Layer.     See  also  Lamina 

of  Baillarger.  Sec  Line  of 
Baillarger 

of  cei'ebellar  cortex,  212 

of  cerebral  cortex,  297-300,  302, 
306-308,  323 

of  Gennari.  See  Line  of 
Gennari 

of  retina,  229,  230,  231 
Learning.     See  Experience,   learn- 
ing by 
Lemniscus  (fillet,  laqueus),  sensory 
fibers  of  the  second  order  ter- 
minating in  the  thalamus 

acoustic.    See  Lemniscus,  lateral 

bulbar,  ascending  sensory  fibers 
of  the  second  order  from  the 
medulla  oblongata  to  the  thal- 
amus, including  several  differ- 
ent tracts,  171 

gustatory.  See  Lemniscus,  vis- 
ceral 

lateral,  the  acoustic  lemniscus, 
fibers  from  the  cochlear  nuclei 
to  the  coUiculus  inferior  anil 
thalamus,  123,  171,  176,  178, 
180,  183,  190,  194,  203,  224 

medial,  ascending  fibers  of  the 
proprioceptive  system  from 
the  spinal  cord  to  the  thala- 
mus, 149,  152,  169,  170,  171, 
176,  178,  179,  180,  183,  190, 
192,  194,  197 

optic,  a  term  which  might  ap- 
propriately replace  optic  Tract, 
233 

spinal,  ascending  fibers  of  toui^h, 
temperature,  and  pain  sensi- 
bility from  the  spinal  cord  to 
the  thalamus.  In  the  conl 
thesc>  fibers  form  t\\-o  tracts, 
the  dorsal  and  ventral  spino- 
thalamic tracts,  142,  145,  150, 
162,  170,  176,  178,  179.  183, 
190,  191.  195,  197,  280,  281 

trigeminal,     ascending     sensory 


372 


INDEX   AND    GLOSSARY 


fibers  of  the  second  order  from 
the  sensory  V  nuclei  to  the 
thalamus,  151,  152,  171,  176, 
178,  179,  180,  183,  190,  191, 
197 
Lemniscus,  visceral,  a  name  sug- 
gested for  ascending  secondary 
fibers  from  the  nucleus  of  the 
fasciculus  solitarius  to  higher 
cerebral  centers,  172,  274 
Lenhossek,  M.  von,  42 
Lens,  228,  232,  235,  236 
Leptomeninges,  the  Arachnoid  and 

Pia  mater 
Lewandovs^sky,  M.,  38,  216,  334 
Leyton,  a.  S.  F.,  317,  334 
Life,  definition  of,  17,  18 
Ligament,  spiral,  of  Cochlea,  219 
Limbus  laminae  spiralis,  219,  221 
Limen  insulse.     See  Nucleus  olfac- 

torius  lateralis,  243 
Line  of  Baillarger,  a  stripe  of  tan- 
gential white  fibers  in  the  cere- 
bral cortex;  there  is  an  outer 
and  an  inner  line,  297,  302 
of  Gennari,  a  stripe  of  tangential 
white  fibers  in  the  Area  striata 
of  the  cerebral  cortex;  it  is  the 
outer  Line  of  Baillarger  in  this 
area,  298,  302 
Lingula  cerebelli,  a  small  eminence 
on   the   ventral   surface   of   the 
cerebellum    where    the    anterior 
medullary  Velum  joins  the  Ver- 
mis, 177,  211 
LissAUER,  tract  of,  zone  of.     See 

Fasciculus  dorso-lateralis 
Lizard,  parietal  eye  of,  236 
Lobe  (lobus),  frontal,  129,  295,  314 
anterior  cerebelli,  209,  210 
of  the  lateral  line   (lobus  linese 
lateralis),  a  highly  differenti- 
ated part  of  the  acoustico-lat- 
eral  Area  of  fishes,  166 
limbic.     See  Gyrus  fornicatus 
occipital,  295,  314 
olfactory  (lobus  olfactorius),  the 
olfactory  Bulb,  its  Crus,  and 
the  anterior  part  of  the  Area 
olfactoTia;  this  is  the  B.  N.  A. 
usage;  the  term  is  sometimes 
applied  to  the  olfactory  Bulb 
alone   and  sometimes  to  the 
Area  olfactoria  alone 


Lobe,  optic.  See  Colliculus  superior 
parietal,  295 

pyriform  (lobus  piriformis),  the 
lateral  exposed  portion  of  the 
olfactory    cerebral    cortex   in 
lower  mammals,  bounded  dor- 
sally  by  the  Fovea  limbica ;  in 
man  it  is  represented  by  the 
Uncus  and  part  of  the  Gyrus 
hippocampi,  243 
temporal,  129,  224,  225,  244,  295 
vagal.     See  Lobe,  visceral 
visceral  (lobus  visceralis,  vagal 
lobe,  lobus  vagi),  the  visceral 
sensory   Area  of  fishes,    162, 
163,  166,  167,  337 
Lobulus  ansiformis,  210 
biventer,  210 
centrahs,  210,  211 
paracentralis,  128 
paramedianus,  209,  210 
parietalis  inferior,  130 

superior,  130 
quadrangularis,  210 
semilunaris,  210 
simplex,  209,  210 
Local  sign ;  cf .  Localization  of  sen- 
sation, 89,  256,  278,  288 
Localization  of  functions  in  central 
nervous    system,    69,     121, 
254-257,  261,  312  ff. 
in  cerebellar  cortex,  208-211, 

339 
in  cerebral  cortex,   208,   306, 
311—328 
of  sensation,  85,  89,  90,  254-257, 
278,  288,  320 
Locomotion,  reflexes  of,  146 
LoEB,  J.,  38,  64,  73 
LowENTHAL,  tract  of.     See  Tract, 

tecto-spinal 
LuciANi,  L.,  14,  216 
LuGARO,  E.,  13,  46,  111 
Lumbricus,  nervous  system  of,  29, 

30 
Lungs,  innervation    of.     See    Re- 
spiratory apparatus 
LuYs,    body    of.     See    body    of 

LUYS 

Lyra.     See  Lyre  of  David 

Lyre  of  David  (lyra  Davidis,  psal- 
teriuni),  the  posterior  part  of  the 
Fornix  body,  including  the  Com- 
missura  hippocampi 


INDEX    AND    GLOSSARY 


373 


Macula  sacculi,  218 

utriculi,  218 
Magendie,  foramen  of.     Sec  Fora- 
men of  Magendie 
Mall,  F.  P.,  135 

Mammals,  cortical  regions  of,  30(5 
Mammillary  body.     See    Body, 

mammillary 
Mantle.     See  Cortex,  cerebral 
Marburg,  O.,  14 
Marchi,  method  of,  50,  146 
Marie,  P.,  334 
Marsupial  animals,  cerebral  cortex 

of,  241 
Massa     intermedia     (commissura 
mollis,  soft  commissure,  middle 
commissure),    a    band    of    gray 
matter    connecting    the    medial 
surfaces    of    the    two    thalami 
across  the  third  ventricle;  it  is 
not    a    true    commissure,    128, 
177 
Mast,  S.  O.,  238 
Mastication,  apparatus  of,  83,  156, 

160,  197,  271,  274 
Matter,   central  gray.     See   Gray, 
central 
gray    (substantia    grisea),    gray 
nervous    tissue    composed 
chiefly     of     nerve-cells     and 
unmyelinated        nerve-fibers, 
116,  138 
white  (substantia  alba),   white 
nervous      tissue      composed 
chiefly  of  myelinated  nerve- 
fibers,  116,  138 
McCoTTER,  R.  E.,  240,  248 
Meatus,  external  auditory,  217 
Medial  (medialis),  nearer  the  me- 
dian plane;  opposed  to  lateral 
Median   (medianus),  lying  in  the 
axis  or  middle  plane  of  the  body 
or  one  of  its  members 
Medius,  intermediate  between  two 

other  parts 
Medulla  oblongata  (bulb),  the 
Myelencephalon  B.  N.  A. ; 
the  older  and  better  usage 
includes  the  whole  of  the 
Rhombencephalon  except 
the  Cerebellum  and  Pons, 
115,  118-120,  125-129,  130, 
131,  155,  166-170,  177,  257, 
271,  337 


Medulla  oblongata,  reflexes  of,  155, 
162,  108,  261,  262,  337 
spinahs.     See  Spinal  cord 
Medullary     sheath.     See     Myelin 
sheath 
lube.     Sec  Neural  tube 
Meis.sner,  corpuscle  of,  88 
plexus   of    (submucovis   plexus), 
66,  268 
Membrane,  basilar,  of  spiral  organ, 
219,  220,  221 
fenestrated',  97,  220 
of  the  brain.     See  Meninges 
limiting,    of   retina    (membrana 
limitans  externa  and  interna), 
231 
mucous,  nerves  of,  95,  137,  160, 

239,  257 
nuclear,  105 
reticular,  220 
Schneiderian.     See    Epithelium, 

olfactory 
tectorial,  219,  220,  221 
tympanic  (drum  membrane),  91, 

217,  218,  272,  277 
vestibular  (membrane  of  Reiss- 
nbr),  219 
Memory,  329,  331,  338,  341,  346 
associative,  33,  68,  269,  328,  329, 
341 
Menidia,  nerves  of,  162,  163,  223 

spinal  cord  of,  164 
Meninges,  the  membranes  of  the 
brain  and  spinal  cord,  133,  160, 
278 
Merkel,  corpuscle  of,  87,  88,  89 
Mesencephalon     (midbrain),     the 
Corpora     quadrigemina     and 
cerebral    Peduncles,    65,    66, 
125-128,  130,   131,   175,    176, 
257 
development  of,  125-128,  175 
Metabolism,  chemical  changes  in 
protoplasm,  102,  103,  105,  179 
Metathalamus,  the  posterior  part 
of  the  Thalamus,  comprising  the 
medial    and    lateral    geniculate 
Bodies,  127,  130,  131,  180,  183 
Metencephalon     (hindbrain),    the 
anterior  part  of  the  Rhomben- 
cephalon, including  the  Cerebel- 
lum, Pons,  and  interv(>ning  part 
of  the  Medulla  oblongata,  126- 
128,  130 


374 


INDEX   AND    GLOSSARY 


Meyer,  A.,  46,  52,  58,  122,  135. 

327,  334 
Meyer,  Max,  291 
Meynert,     commissure    of.     Sec 
Commissure,  postoptic 
decussation  of  (fountain  decussa- 
tion, dorsal  tegmental  decussa- 
tion), 143,  176 
fasciculus     retroflexus    of.     See 
Tract,  habenulo-peduncular 
Michelson,  a.  a.,  76 
Midbrain.     See  Mesencephalon 
MiLLIKAN,  R.  A.,  76 
Mind.     See  Consciousness 

evolution  of.     See  Psychogene- 

sis 
unconscious,  330,  331 
Mitochondria,  49 

Molecular    substance,    Molecular 
layers,  a  name  applied  to  the 
Neuropil 
MOLHANT,  M.,  276 
MoNAKOw,  C.  VON,  187,  321,  327, 
334 
tract  of.    See  Tract,  rubro-spinal 
Monkey,  cerebral  cortex  of,  312 
Monro,  foramen  of.     See  Foramen 

interventriculare 
MooDiE,  Roy  L.,  124 
Moon-eye,  brain  of,  337 
Morals,  348,  349,  350 
MoRGULis,  S.,  269,  276 
Morris,  14 

Motor  apparatus,  65,  66,  129,  168, 
179,  198-199,  203,  214,  261,  271, 
274,  289,  314-318,  344 
MoYES,  J.  M.,  309 
Mucous  membrane,  nerve  endings 

in.     See  Membrane,  mucous 
MtJLLER,  fibers  of,  229,  230 
Multiple  consciousness,  330 
MuNK,  H.,  334 
Muscarin,  258 

Muscle,    Muscles,  of  arm,  motor 

nuclei  of,  140 

cardiac,  the  muscle  of  the  heart, 

a  visceral  muscle  whose  fibers 

are  cross-striated,  99, 162,  249, 

261 

of  eyeball.     See  Eye,  muscles  of 

of  facial  expression,  innervation 

of,  156,  160,  271,  289 
intercostal,  innervation  of,  263- 
268 


Muscle,  involuntary,  muscles  not 

under  direct  control  of  the  will ; 

thev  are  of  the  general  visceral 

type,  98,  99 

nerve  endings  in,  41,  92,  95,  98, 

99 
respiratory,  263-268 
sense,  82,  92,  143,  149,  152,  160, 

192-198,  270 
skeletal.     See  Muscle,  somatic 
smooth  or   unstriated,    visceral 
muscle  whose   fibers  are  not 
cross-striated,  92,  99,  161,  162 
somatic,  striated  muscles  derived 
from     the     Somites    of    the 
embryo,  skeletal  muscles,  41, 
92,  98,  158-161, 
spindle,    a    bundle    of    muscle- 
fibers,  smaller  than  ordinary 
fibers,  which  are  supplied  with 
special  nerve  endings  of  the 
muscle    sense  in  addition  to 
typical  motor  End-plates,  92 
sternocleidomastoid,  156,  161 
striated,  composed  of  fibers  hav- 
ing a  cross-striped  appearance; 
may  be  somatic  or  visceral,  41, 
92,  98,  99 
synergic,     muscles    which    act 
together  for  the  performance 
of  a  movement,  36,  340 
of  tongue.     See  Tongue,  muscles 

of  . 

trapezius,    innervation   of,    156, 

161 

visceral,  unstriated  or  striated 

muscles  not  derived  from  the 

Somites  of  the  embryo;  may 

be  involuntary  or  voluntary, 

92,  98,  99,  137,  162,  249 

voluntary,  muscles  under  direct 

control  of  the   will;  may  be 

either  somatic  or  visceral,  98 

Mustelus,  nervous  system  of,  119, 

120 
Mycetozoa,  23 

My  el  (myelon),  the  Spinal  cord 
Myelencephalon  (afterbrain),  the 
posterior  part  of  the  Rhomben- 
cephalon, or  that  portion  of  the 
Medulla  oblongata  lying  behind 
the  Pons  and  Cerebellum,  126, 
127,  128,  130,  131 
Myelin,  a  fat-like  substance  formed 


INDEX    AND    GLOSSARY 


375 


as  a  sheath  around  the  mye- 
linated    (medullated)     nerve- 
fibers,  49 
Myelin    sheath,    an    envelope    of 
Myelin  around  the  Axis -cylin- 
der of  some  nerve-fibers,  41, 
49,  116,  320 
Myelogeny,  the  sequence  of  matur- 
ation of  the  Myelin  sheaths  of 
nerve-filiers  in  the  development 
of  the  central  nervous  system, 
320,  321,  322 
Myelon  (mycl),  the  Spinal  cord 
Myotom.     See  Somites 
Myxomycetes,  23 

Nates.     See  Colliculus  superior 
Nausea,  apparatus  of,  95,  270 
Necturus,  nervous  system  of,  65,  66 
Neencephalon,  the  new  brain,  i.  e., 
the     cerebral     cortex     and    its 
dependencies,  124,  292 
Negative  variation  in  nerve-fibers, 

102 
Nemiloff,  a.,  49,  58 
Neopallium,  the  non-olfactory  part 
of  the  cerebral  cortex,  or  somatic 
cortex,  241,  244,  246 
Neothalamus  (new  thalamus),  the 
phylogenetically  new  part  of  the 
Thalamus,  which   is   a  cortical 
dependency,  17^183,  292,  340 
Nerve    (nervus),    any    bundle    of 
nerve-fibers  outside  the  central 
nervous  system,  29,  114 
abducens  (VI  cranial  nerve),  123, 
129,  155,  157,  159,  160,  164, 
197,  204 
accelerator,  of  heart,  261,  262 
accessory    (XI    cranial    nerve), 

129,  156,  161,  162,  271 
acoustic     (VIII    cranial    nerve, 
auditorv  nerve,  nervus  acusti- 
cus),    118,  119,  120,  123,  129, 
155,   158,   159,   161,    163,  164, 
201,  219,  221,  223,  224 
afferent.     See  Afferent 
anterior  cutaneous,  136 
auditory.     See    Nerve,   acoustic 
auricular,  156,  161 
branchial,  118, 119,  121,  163,  273 
buccal,  223 

cardiac.     See  Heart,  innervation 
of 


Xcive,  cerebral.   See  Nerve,  cranial 

cerebro-spinal,  the  periplieral 
nerves  connected  with  the 
brain  and  spinal  cord,  114,  115 

cervical,  115,  141 

chorda  tympani,  160,  272 

ciliary,  160 

coccygeal,  115 

cochlear,  159,  171,  201,  203,  219, 
221,  222,  223 

components,  158-162 

cranial  (cerebral  nerve),  a  periph- 
eral nerve  connected  with 
the  brain;  these  nerves  are 
enumerated  in  12  pairs,  114, 
118-120,  155-168,  178,  271, 
272 
of  fishes,  118-120,  162,  163 

cutaneous,  84-91,  136,  143,  145, 
156,  159-163,  171,  189-198, 
254,  280,  281 

of  Cyon,  262 

of  deep  sensibility;  cf.  Proprio- 
ceptors, apparatus  of,  84,  92, 
143,  189,  192-198 

depressor,  of  heart,  262 

efferent.     See  Efferent 

excito-glandular,  98,  116 

facial  (VII  cranial  nerve,  faci- 
ahs),  118,  119,  120,  123,  129, 
156,  158,  159,  160,  162,  163, 
164,  256,  264,  271-274 

glossopharyngeal  (IX  cranial 
nerve),  118, 119, 120, 123,  129, 
156,  158,  159,  161-164,  168, 
169,  256,  271-274 

gustatory,  270-274 

hyomandibular,  118,  119,  120, 
163 

hypoglossus  (XII  cranial  nerve), 
129,  156,  159,  161,  164,  167, 
170 

inhibitory,  a  nerve  which  checks 
or  retards  the  action  of  the 
organ  in  which  it  terminates, 
116,  261,  262 

intercostal,  136,  263,  264 

intermediate  (nerve  of  Wris- 
BERG,  pars  intermedia  facialis, 
.  portio  intermedia  facialis,  the 
smaller  of  the  two  roots  of  the 
VII  cranial  nerve),  123,  129, 
160,  271,  272 

intestinal,  119,  163 


376 


INDEX   AND    GLOSSARY 


Nerve   of  Jacobson,     See  Nerve, 
tympanic 
of  Lancisi.     See  Stria  longitudi- 

nalts 
laryngeal,  161 

lateral  (nervus  lateralis,  lateral 
line  nerves),  branches  of  the 
VII,     IX,    and    X    cranial 
nerves    which    supply    the 
Lateral    line    organs,    118, 
119,  120,  159,  162,  163,  166, 
222,  223 
accessory  (ramus  lateralis  ac- 
cessorius  facialis),  163,  273 
cutaneous,  136 
lingual,  161,  272 
lumbar,  115,  256 
mandibular,  118,  119,  160,  223, 

272 
maxillary,  118, 118,  160,  251,272 
motor,  a  peripheral  nerve  which 
conducts  efferent  impulses  to 
a  muscle,  116,  159-165 
oculomotor  (III  cranial  nerve), 
123,  129,  155,  157,  159,  160, 
164,   175,  176,  197,  204,  234, 
256,  274 
olf acto  ry   (nervus    olf actorius , 
the    first    cranial   nerve),    97, 

118,  119,  120,  155,  160,  162, 
163,  164,  175,  223,  239-242, 
293 

ophthalmic,  118,  119,  120,  160, 
163,  223,  272 

optic  (nervus  opticus,  the  second 
cranial  nerve);  this  is  not  a 
true  nerve,  but,  in  reality,  a 
cerebral  tract;  cf.  Tract,  optic, 

119,  120,  129,  132,  155,  157, 
159,  160,  163,  164,  180,  223, 
228,  229,  232,  233,  234 

otic,  163 

of  pain,  277,  279,  280,  281,  285, 
■  287 

palatine,  a  nerve  of  fishes  corre- 
sponding to  the  human  great 
superficial  petrosal  nerve,  118, 
119,  120,  163 

parietal  (nerve  of  the  Parietal 
eye),  236,  237 

phrenic,  263,  264,  265,  266 

pneumogastric.  See  Nerve,  vagus 

postganglionic.  See  Neuron, 
postganglionic 


Nerve,  preganglionic.    See  Neuron, 
preganglionic 

prespir  acular  (pretrematic 
branch  of  the  facial),  119,  163 

pretrematic,  of  facial,  119,  163 

recurrent,  251 

sacral,  115,  256,  257 

sciatic,  103 

sensory,  a  peripheral  nerve 
which  conducts  afferent  im- 
pulses from  a  sense  organ  to 
the  spinal  cord  or  brain,  116, 
137 

somatic,  137,  150,  158,  159,  164, 
189 

spinal,  a  peripheral  nerve  con- 
nected with  the  spinal  cord, 
114,  115,  123,  136,  137 
central  connections  of,  136- 
153,  164,  165,  279,  280,  281 
components  of,  137,  159,  161, 
164,  165 

splanchnic,  251 

superficial  petrosal,  161,  272 

supratemporal,  163 

sympathetic.  See  Nervous  sys- 
tem, sympathetic 

of  taste.  See  Gustatory  appara- 
tus 

terminal,  a  slender  nerve  associ- 
ated with  the  olfactory  nerve, 
119,  161,  239 

thoracic,  115,  136,  137,  141,  256, 
257,  263 

trigeminal  (trifacial  nerve,  V 
cranial  nerve),  118,  119,  120, 
123,  129,  152,  156,  158-160, 
162,  163,  164,  166,  168,  171, 
178,  191,  194,  198,  271,  272, 
273 

trochlear  (patheticus,  IV  cranial 
nerve),  118, 123, 129,  155,  157, 
159,  160,  164,  168,  197,  204 

tympanic  (nerve  of  Jacobson), 
161,  272 

vagus  (pneumogastric  nerve,  X 
cranial  nerve),  118,  119,  120, 
123,  129,  156,  158,  161-170, 
251,  256,  261-274 

vasoconstrictor,  262 

vasodilator,  262 

vasomotor.  See  Vasomotor  ap- 
paratus 

vestibular,  93,  94,  118,  119,  158, 


INDEX    AND    GLOSSARY 


377 


159,    161,    1(54,    194,   201-204, 
206,  223,  224 

Nerve,  vidian,  272 

visceral,  137,  156-170,  249-276, 

288 
vomero-nasal,  240 
of  Wrisbbrg.     See  Nerve,  inter- 
mediate 
Nerve-cell.     See  Neuron 
Nerve-fiber,  a  slender  fibrous  proc- 
ess of  a  Neuron,  40 
afferent,  116 
carbon  dioxid  production  in,  102, 

103 
conduction  in,  102,  103 
degeneration  of,  50 
efferent;  cf.  also  Efferent,  116 
electric  changes  in,  102 
fatigue  of,  102,  107-110 
medullated.     See    Nerve-fiber, 

myelinated 
myelinated,  a  fiber  provided  with 
a  Myelin  sheath,  103,  116,  320 
postganglionic.     See    Neuron, 

postgangUonic 
preganglionic.    See  Neuron,  pre- 
ganglionic 
rate  of  transmission  in,  103,  104 
regeneration  of,  50 
unmyelinated  or  unmedullated, 
a   fiber    devoid   of   a    Myelin 
sheath,  116 
Nervous  impulse,  nature  of,   102, 
103 
velocity  of,  103,  104 
Nervous  system,  the  aggregate  of 
all  nervous  tissues 
autonomic;   cf.    Nervous  sys- 
tem, sympathetic,  249-259 
central,  29,  114,  115 
cerebro-spinal,  81,  250 
cerebro-spinal,  visceral,  252 
development  of,  114,  125-128, 
165,  167,  199,  228,  243,  320- 
324 
diffuse,  28,  55,  69,  252,  279 
•embryonic.     See  Nervous  sys- 
tem, development  of 
evolution  of;  see  also    Cortex, 
cerebral,   evolution  of,  and 
Hemisphere,  cerebral,  com- 
parative anatomy  and  evo- 
lution of,  23,  25,  "28,  34,  35, 
121,  124,  140,  198,  199,  236, 


239-241,  252,  279-281,  292, 
335  ff. 

Nervous  system,  general  anatomy 
of,  114 
invertebrate,  28-35,  55,  252 
nomenclature  of,  124,130-132, 

138,  139,  183 
peripheral,  114 
phytogeny    of.     See    Nervous 

system,  evolution  of 
physiology  of,  102 
segmental.     See  Segmentation 

and  Segmental  apparatus 
subdivision  of,  114,  124-132 
sympathetic,  56,  69,  81,  93,  98, 
114,    115,   136,   137,   158, 
161,    162,  164,  235,  249- 
258,  261-274,  283,  288 
peripheral  autonomous  part, 
252 
synaptic,  55 
vertebrate,  30,  114 
Nervus.     See  Nerve 
Neural  canal.     See  Canal,  neural 
groove   (medullary  groove),  the 
trough-like  form  assumed  by 
the  Neural  plate  during  its  in- 
vagination to  form  the  Neural 
tube 
plate,  a  thickened  plate  of  Ecto- 
derm in  early  vertebrate  em- 
bryos from  which  the  Neural 
tuije  develops 
tube,  the  embryonic  central  ner- 
vous system  when  in  the  form 
of  an  epithelial  tube,  114,  125, 
126,  137,  175,  199 
Neuraxis,  the  central  nerA^ous  sj's- 
tem;    also    applied'to  the  Axon 
Neuraxon.     See  Axon 
Neurenteric  canal,  in  the  embryo, 
a    communication    between    the 
caudal  end  of  the  Neural  tube 
and  the  digestive  tract 
Neurilemma,  the  outer  sheath  of  a 

peripheral  nerve-fiber,  41,  49 
Neurite.     See  Axon 
Neurobiotaxis,  112 
Neuroblast,    an    immature    nerve 

cell,  40,  46 
Neurocyte.     See  Neuron 
Neurofibrils,  delicate  protoplasmic 
fibrils  within   the   cytoplasm   of 
the  Neuron,  42,  48,  49,  108 


378 


INDEX    AND    GLOSSARY 


Neuroglia  (glia),  a  supporting  fab- 
ric of  cells  and  horny  fibers  per- 
vading the  central  nervous 
system,  39,  111,  212,  229,  230, 
298 
Neurogram,  329 
Neuromasts.     See  Organs,  lateral 

line 
Neuromere,  one  of  the  segments  of 

the  embryonic  Neural  tube 
Neuron  (neurocyte),  a  nerve  cell; 
cf.  Cell,  39-57,  102,  212,  298- 
302 
afferent,  44 
bipolar,  46 

correlation,  144,  145,  172 
efferent,  44 

fatigue  of,  102,  107-110 
of  first,  second,  etc.,  order,  44 
lower  motor,  317 
multiform.     See    Neuron,    poly- 
morphic 
polarization  of.     See  Polarity  of 

the  Neuron 
polymorphic,  298,  301,  302 
postganglionic,  an  efferent  sym- 
pathetic neuron  which  is  ex- 
cited by  a  preganglionic  Neu- 
ron,   98,    137,    160-162,    164, 
256,  258,  262,  265,  267,  271 
preganglionic,  an  efferent  sympa- 
thetic neuron  whose  cell  body 
lies  in  the  central  nervous  sys- 
tem,   98,    137,    160-162,    164, 
256,  258,  261,  262,  265,  267, 
271 
pyramidal,  of  cerebral  cortex,  43, 

45,  298,  299,  301,  302,  323 
retraction  of,  111 
type  I,  45,  46,  212 
type  II,  45,  46,  212,  298,  301 
unipolar,  46 
upper  motor,  317 
Neurone.     See  Neuron 
Neuropil  (molecular  substance,  dot- 
ted substance),  an  entanglement 
of  unmyelinated  fibers  contain- 
ing many  synapses,  69 
Neuropore,  in  the  embryonic  brain 
an  opening  between  the  anterior' 
end  of  the  neural  Canal  and  the 
exterior,  125 
Nicotin,  256 
Nidulus,  116 


Nidus,  a  depression  on  the  ventral 
surface  of  the  cerebellum;  also 
used  as  a  synonym  for  Nucleus 
(2),  116 

NissL,  F.,  43,  47,  58,  302 
bodies  of,  granules  of,  substance 
of.     See  Substance,  chromo- 
phiiic 

Nociceptor,  a  sense  organ  or  Recep- 
tor which  responds  to  injurious 
influences 

Node  of  Ranvier,  an  interruption  of 
the  Myelin  sheath  of  a  nerve- 
fiber,  41 

Node,  vital,  266 

Nodulus,  209,  210,  211 

Nomenclature.  See  Nervous  sys- 
tem, nomenclature  of 

Nose.     See  Olfactory  apparatus 

Nose  brain  (Rhinencephalon),  121, 
132 

Nucleus  (1),  the  differentiated  cen- 
tral protoplasm  of  a  cell,  40,  41, 
42,  48,  102,  105,  108,  109,  116 

Nucleus  (2),  a  group  of  nerve-cells 
within  the  central  nervous  sys- 
tem; also  called  Nidulus  and 
Nidus;  cf.  Ganglion,  116 
of  abducens  nerve,  63,  160,  164, 

168,  203,  224 

acoustic.     See  Nucleus,  cochlear 
ambiguus,    161,    164,    167,    168, 

169,  170,  203,  271 
amygdalae    (amygdala),   a  small 

mass  of  subcortical  gray  mat- 
ter under  the  tip  of  the  tem- 
poral lobe  which  forms  part  of 
the  Nucleus  olfactorius  later- 
alis, 181,  306 

anterior  thalami,  179,  180,  181, 
183,  240,  244 

arcuate,  169 

of  auditory  nerve.  See  Nucleus, 
cochlear,  and  Nucleus,  vestibu- 
lar 

of  Bechterew,  vestibular,  202, 
203 

caudate  (nucleus  caudatus), 
one  of  the  two  large  gray 
masses  of  the  Corpus  stri- 
atum, 123,  177,  181,  184,  186, 
246 

of  Clarke.  See  Nucleus,  dorsal, 
of  Clarke 


INDEX    AND    (iliOSSAHV 


379 


Nucleus,  cochloar,  63,  66,  Kit,  168, 
171,  178,  203,  224 

commissural,  of  C'a.ial,  2(J2,  178, 
266,  271,  274 

of  Deiters,  vestibular,  202, 
203 

dentate,  a  large  micleus  eml)ed- 
ded  within  the  cerebellar 
hemisphere  from  which  the 
fibers  of  the  Brachium  con- 
junctivum  arise,  123,  205,  213, 
224 

dorsal,  of  Clarke  (nucleus  dor- 
salis  of  Clarke  or  Stilling, 
Clarke's  column),  a  longitu- 
dinal strand  of  neurons  of  the 
spinal  cord  whose  axons  enter 
the  spino-cerebellar  tracts,  142, 
149,  150,  194 

of  dorsal  funiculus.  See  Clava 
and  Tuberculum  cuneatum 

dorsal,  of  vagus.  See  Nucleus  of 
vagus,  dorsal 

dorsalis  thalami.  See  Nucleus 
anterior  thalami 

dor  so -lateral,  of  spinal  cord,  a 
collection  of  neurons  in  the 
ventral  gray  column  which  in- 
nervate the  muscles  of  the 
limbs,  141 

of  Edinger-Westphal,  the  vis- 
ceral efferent  nucleus  of  the 
oculomotor  nerve,  160,  164, 
168,  274 

emboliformis,  213,  224 

of  facial  nerve,  160,  164,  168, 
271 

of  fasciculus  cuneatus.  See  Tu- 
berculum cuneatum 

of  fasciculus  gracilis.     See  Clava 

of  fasciculus  solitarius,  the  vis- 
ceral sensory  nucleus  of  the 
VII,  IX,  ancl  X  cranial  nerves, 
164,  168,  169,  170,  261,  264, 
266,  267,  270,  271,  274 

fastigii,  213,  224 

giobosus,  213 

of  glossopharvngeus  nerve,  IGl, 
164 

habenula;.     See  Habenula 

of  hvpoglossus  nerve,  161,  164, 
167,  168,  170 

interpeduncular,  a  nucleus  lying 
between  the  cerebral  peduncles 


wliicli   receives  the  habenulo- 

peduncular  tract 
Nucleus,  of  lateral  lemniscus,  203, 

224 
lateralis  thalami,   178-183,   185, 

190,  193,  194,  282,"  319,  341 
lattice,       of       thalamus.      See 

Nucleus  reticularis  thalami 
lentiform    (nucleus    lentiformis, 

lenticular  nucleus),  one  of  the 

two  large  gray  masses  of  the 

Corpus    striatum,     123,     181, 

184,  186 
magnocellularis  tecti.     See  Nu- 
cleus,    mesencephalic,     of     V 

nerve 
masticatory.     See     Nucleus     of 

trigeminus,  motor 
medialis  thalami,  178,  179,  181, 

183,  185,  190,  194,  341 
mesencephalic,  of  V  nerve,  160, 

168,  176,  178,  197 
motorius  tegmenti,  199 
of  oculomotor  nerve,  65,  66,  160, 

162,   168,  175,  176,  203,  234, 

235,  274 
olfactorius  anterior,  the  anterior 
undifferentiated  portion  of 
the  Area  olfactoria,  244 

intermedins.  See  Tuberculum 
olfactorium 

lateralis,  the  lateral  portion  of 
the  Area  olfactoria,  lying  be- 
tween the  olfactory  Bulb 
and  the  Uncus,  243 

medialis,  the  medial  portion  of 
the  Area  olfactoria,  contain- 
ing the  Septum  and  Gyrus 
subcallosus,  243 
olivary.     See  Olive 
of  origin,  a  nucleus  from  which  a 

fiber  tract  arises,  117,  139 
pontile     (pontile    nuclei,    nuclei 

pontis),  173,  205,  206,  323 
posterior  thalami,  178,  179,  180, 

183 
preoptic       (ganglion       opticum 

basale),  244 
red.     See  Nucleus  ruber 
reticularis     thalami      (lattice 

nucleus,  Gitterschicht),  341 
roof,  of  cerebelhmi    (nuclei  fas- 
tigii, giobosus,  and  embolifor- 
mis), 206,  213,  224 


380 


INDEX   AND    GLOSSARY 


Nucleus,  ruber  (red  nucleus),  173, 
176,  180,  205,  206,  234,  323 
salivatory,    160,    161,    168,    170, 

269,  271,  274 
of    ScHWALBE,    vestibular,    202, 

203 
of  Stilling.     See  Nucleus,  dor- 
sal, of  Clarke 
terminal,  a  nucleus  into  which  a 
fiber  tract  discharges,  117,  139 
of  trigeminus,  chief  sensory,  163, 
168,  171,  178,  190,  198,  271 
motor,  160,  162,  168,  198,  271 
spinal    (nucleus    of    spinal    V 
tract;  old  term,   gelatinous 
substance    of    Rolando    of 
medulla     oblongata),     163, 
168,  169,  170,  171,  178,  190, 
198,  271 
of  trochlear  nerve,  160,  164,  168, 

175,  203,  224,  235 
of  vagus,  dorsal,  161,  164,  168, 

169,  170,  261,  264,  267,  271 
of  ventral  gray  column  of  spinal 

cord,  140,  141 

ventralis  thalami,  178,  179,  180, 
181,  183,  190,  193,  194,  282, 
319,  341 

ventre -lateral,  of  spinal  cord,  a 
collection  of  neurons  in  the 
ventral  gray  column  which  in- 
nervate the  muscles  of  the 
limbs,  140,  141 

ventro-medial,  of  the  spinal  cord, 
a  collection  of  neurons  in  the 
ventral  gray  column  which  in- 
nervate the  muscles  of  the 
trunk 

vestibular,    155,    159,    168,    169, 

170,  178,  194,  202,  203,  204, 
224 

NuEL,  J.  P.,  238 
Number  of  Betz  cells,  316 

of  fibers  in  human  pyramidal 
tract,  316 

of  neurons  in  cerebral  cortex,  27 

Obersteiner,  H.,  34,  298 
Oblongata.  See  Medulla  oblon- 
gata 
Olfactory  apparatus.  See  also  Rhi- 
nencephalon,  77,  79,  92,  97,  118, 
119,  120,  160,  162,  175,  177, 
179,  239-247,  306,  311 


Olive,  accessory,  169 
inferior  (oliva,  nucleus  olivaris, 
olivary   body),    a   large   gray 
center  in  the  medulla  oblon- 
gata which  produces  an  emi- 
nence on  its  lateral  surface, 
123,  131,  169,  170,  172,  190, 
194 
superior,  a  nucleus  in  the  second- 
ary auditory  path  embedded 
in    the    medulla    oblongata 
dorsally  of  the  pons,  63, 178, 
203,  224 
peduncle  of,  224 
Onup,  B.,  260 

Operculum,  the  lobules  of  the  fron- 
tal, parietal,  and  temporal  cere- 
bral cortex  which  cover  the  In- 
sula, 130,  184,  295 
Ophthalmencephalon,    the   retina, 
optic  nerve,  and  visual  apparatus 
of  the  brain 
Opossum,  cerebral  cortex  of,  241 
Optic  apparatus.     See  Visual  ap- 
paratus 
chiasma.     See  Chiasma,  optic 
Optic  tectum,  an  optic  reflex  center 
in  the  roof  of  the  midbrain. 
See  Colliculus,  superior 
thalamus.     See  Diencephalon 
vesicle.    See  Vesicle,  optic 
Oral,  pertaining  to  the  mouth,  or 
directed  toward  the  mouth,  as 
opposed  to  Caudal 
sense  of  Edinger,  245 
Organ    (organon),   a   part  of   the 
body  with  a  particular  func- 
tion, 25 
of  CoRTi.     See  Organ,  spiral 
generative.     See  Sexual  organs 
lateral  line  (neuromasts),  sense 
organs  in  or  under  the  skin  of 
fishes  and  amphibians  of  inter- 
mediate type  between  tactile 
and  auditory  organsf  118-120, 
159,  162,  163,  166,  222,  223 
parietal.     See  Parietal  eye 
pineal.     See  Body,  pineal 
spiral  (organon  spirale),  the  or- 
gan of  CoRTi  or  receptor  for 
sound  in  the  Cochlea,  92,  219- 
222 
vomero-nasal   i^organ  of  Jacob- 
son),  240 


INDEX    AND    (JL(JSSAKY 


381 


Ossicles,  auditory,  217,  218 
Oxydation    in   neurons,    102,   10;3, 
105 

Pachymeninges,   the  Dura  mater 

Pacinian  corpuscle,  85,  93 

Pain,  apparatus  of;  cf.   Affection, 

90,  95,  142,  143,  149,  150,  151, 

182,    189-192,    196,    253-256, 

270,  277-290,  320 

conduction  paths  for,  263,  277, 

279-283,  285-287 
referred,  253-256 
thalamic  center  for.     See  Thala- 
mus, pain  center  in 

Palaeencephalon,  the  old  brain,  i.  e., 
all  of  the  brain  except  the  cere- 
bral cortex  and  its  dependencies, 
124,  292 

Palaeothalamus  (old  thalamus),  the 
phylogenetically  old  part  of  the 
Thalamus,  present  in  animals 
which  lack  the  cerebral  cortex, 
179,  181 

Palate,  272 

Pallium.  See  Cortex,  cerebral, 
240 

Pancreas,  249 

Paralysis  from  central  lesion,  191, 
195,  316-318,  320 

Paraphysis,  an  evagination  of  the 
membranous  roof  of  the  telen- 
cephalon in  front  of  the  Velum 
transversum  in  some  vertebrate 
brains 

Parietal  eye  (parietal  organ,  pineal 
eye,  epiphyseal  eye),  a  modifica- 
tion of  the  pineal  Body  in  some 
lower  vertebrates  to  form  a  dor- 
sal median  eve,  177,  236,  237 

Parker,  G.  H.,  38,  80,  100,  101, 
222,  226,  236,  237,  238,  350 

Parmelee,  M.,  38 

Pars  intermedia  of  Wrisberg.  See 
Nerve,  intermediate 

Pars  mamillaris  hypothalmi,  the 
mammillary  bodies  and  their 
environs,  127 
optica  hypothalami,  the  optic 
Chiasma  and  its  environs,  127, 
130,  132 

Pause,  central,  104 

Pawlow,  I.,  269,  276 

Pedagogy.     See  Education 


Peduncle  (pedunculus),  a  peduncle 
or  stalk.  Sec  Crus 
cerebellar,  one  of  the  fibrous 
stalks  by  which  the  cerebellum 
is  attached  to  the  brain  stem. 
There  are  three  peduncles  on 
each  side:  (1)  the  superior  ped- 
uncle (Brachium  coniuncti- 
vum),  (2)  the  middle  peduncle 
(Brachium  pontis),  (3)  the  in- 
ferior peduncle  (Corpus  resti- 
forme),  173,  205,  206 
cerebral  (pedunculus  cerebri), 
the  ventral  part  of  the  mesen- 
cephalon, 127-129,  130,  173, 
175,  176 
of  corpus  callosum.     See  Gyrus 

subcallosus 
of  superior  olive,  224 
Perikaryon,    the   protoplasm    sur- 
rounding   the  nucleus  in  the 
Cell  body  of  a  Neuron 
functions  of,  105 
Perilymph,  218 

Perineureum,  the  connective-tissue 
sheath  surrounding  a  peripheral 
nerve 
Peristalsis,  268 
Peritoneum,  85,  278 
Pes  pedunculi.     See  Basis  pedun- 

culi 
Pharynx,  innervation  of,  156,  161, 

272 
Philippson,  M.,  144,  146,  154 
Photoreceptors,       nervous      End- 
organs  sensitive  to  light,  237 
Phrenology,  312,  313 
Phylogeny  of  nervous  system.     See 

Nervous  system,  evolution  of 
Physiognomy,  312 
Pia  mater,  the  inner  brain  mem- 
brane, 133 
Pigment,  retinal.     See  Retina,  pig- 
ment of 
Pike,  F.  H.,  68,  73,  216 
Pillar  of  CoRTi,  219,  220 
of   fornix.     See   Fornix   column 
and  Fornix  crus 
Pilocarpin,  258 
Pineal  body.     See  Body,  pineal 

eye.     See  Parietal  eye 
Pituitary  body.     See  Hypophysis 
Plants    contrasted  with    animals, 
23 


382 


INDEX    AND    GLOSSARY 


Plasticity       in      behavior.      See 

Behavior,  variable 
Plate    (lamina),    a    general   term 
applied  to  any  flat  structure 
or  layer ;  specifically  to  the  six 
longitudinal   bands   or   zones 
into  which  the  Neural  tube  is 
divided  as  explained  in  the  fol- 
lowing definitions,  126 
dorsal  (roof  plate,   Deckplatte), 
the  unpaired  dorsal  longitudi- 
nal epithelial  zone  of  the  Neu- 
ral tube;  it  is  non-nervous  and 
in  some  parts  of  the  adult  brain 
is  enlarged  to  form  a  lamina 
epitheliaUs,  133,  167 
dorso-lateral    (alar   plate,    wing 
plate,    epencephalic     region, 
Fliigelplatte),  one  of  a  pair  of 
dorso-lateral    longitudinal 
zones  of  the  Neural  tube;  it 
gives  rise  to  the  dorsal  gray 
column  of  the  spinal  cord  and 
to  the  sensory  centers  of  the 
brain,  126,  129,  167 
floor.     See  Plate,  ventral 
neural.     See  Neural  plate 
roof.     See  Plate,  dorsal 
ventral     (floor     plate,     Boden- 
platte),  the  unpaired  ventral 
longitudinal  zone  of  the  Neu- 
ral tube;  it  is  originalh^  non- 
nervous,  but  in  the  adult  is 
invaded  by  the  ventral  Com- 
missure, 167 
ventro-lateral   (basal   plate, 
hypencephalic    region,    Bo- 
denpatte),    one  of    a   pair  of 
ventro-lateral       longitudinal 
zones  of  the  Neural  tube;  it 
gives  rise  to  the  ventral  gray 
column  of  the  cord  and  to  the 
motor   centers   of   the   brain, 
126,  129,  167 
Playj  286 

Pleasantness,  Pleasure.    See  Affec- 
tion 
Pleura,  136,  278 

Plexus,  choroid  (plexus  chorioid- 
eus),  highly  vascular  Pia 
mater  attached  to  non-nerv- 
.  ous  epithelial  plates  which 
are  crumpled  and  thrust 
into  the  brain  Ventricles,  133 


Plexus,  lateral,  the  choroid  plexuses 
of  the  lateral  ventricles  of 
the    cerebral    hemispheres, 
133,  246 
of  fourth  ventricle  (plexus  cho- 
rioideus  ventriculi   quarti), 
the   choroid     plexus  which 
forms  the  roof  of  the  fourth 
ventricle,  133 
of  third  ventricle  (plexus  chori- 
oideus  ventriculi  tertii),  the 
choroid  plexus  which  forms 
the  roof  of  the  third  ven- 
tricle, 133,  177,  181 
ganglionic,  of  sympathetic  nerv- 
ous system,  an  entanglement 
of    sympathetic    nerves    and 
ganglion    cells;    most    of    the 
nervous  plexuses  enumerated 
in  the  following  list  are  gangli- 
onic plexuses  of  this  type,  250, 
251,  268 
nervous,  an  interlacing  of  differ- 
ent kinds  of  nerve-fibers,  56 
aortic,  251 

of  AuE  REACH  (myenteric  plex- 
us), 268 
brachial,  251 
bronchial,  261,  265 
cardiac,  251,  262 
celiac,  251 
cervical,  251 
coronary,  251 
esophageal,  251 
gastric,  251,  267 
hypogastric,  251 
lumbar,  251 
of    Meissner    (submucous 

plexus),  56,  268 
mesenteric,  251 
myenteric    (plexus   of    Auer- 

bach),  268 
pelvic,  251 
pharyngeal,  251 
sacral,  251 

solar.     See  Plexus,  celiac 
submucous  (plexus  of  Meiss- 
ner), 56,  268 
vesical,  251 
Poisons,  susceptibiUty  of  neurones 

to,  103,  108-110,  256,  258,  286 
Polarity  of  the  neuron,  40,  55,  103 
POLTMANTI,  O.,  146,  154 
Pons  (pons  Varolii),  a  projection 


INDEX    AND    GLOSSARY 


383 


from  the  under  surface  of  the 
medulla  oblongata  below  the 
cerebellum,  123,  127-129,  130, 
131,   155,   168,  173,  205,  206. 
208 
Pons,  nuclei  of.     See  Nucleus,  pon- 
tile 
Portio  dura  facialis   (inotor  facial 
root),  160 
intermedia.     See    Xervc.    inter- 
mediate 
major  trigemini  (sensor}-  root  of 

the  trigeminus),  160 
minor  trigemini   (motor  root  of 
the  trigeminus),  160 
Posterior,   as   used    in   this    work 
means  toward  the  tail  end  of  the 
body;  as  used  in  the  B.   X.   A. 
tables  it  means  toward  the  dorsal 
side,  125 
Posture,  apparatus  of,  82,  93,  149, 

282 
Precuneus,  128 

Prextiss,  C.  W.,  220,  221,  226 
Pressure,  apparatus  of.   See  Touch 
Primitive  sheath.     See   Neuri- 
lemma 
Prixce,  Morton,  329,  330,  334 
Prionotus  carolinus,  nervous  svs- 

tem  of,  167 
Process, .  axis-cylinder.     See  Axon 
ciliarv,  of  eveball,  155,  160,  257, 

274 
protoplasmic.     See  Dendrite 
Processus  reticularis,  the  Formatio 
reticularis    of    the    spinal    cord, 
138,  140 
Projection  centers,  those  parts  of 
the  cerebral  cortex  which  re- 
ceive or  give  rise  to  Projection 
fibers;    cf.     Center,    cortical, 
181.   306,   315,   316,  317-323, 
340 
fibers,  fibers  which  connect  the 
cerebral  cortex  with  the  brain 
stem,  178,  180,  181,  183,  185, 
296.  297,  298,  318-323 
Proprioceptor,  a  sense  organ  lying 
within  the  deep  tissues  of  the 
body  for  the  coordination  of 
somatic  reactions,  82.  92 
apparatus  of,  141-143.  148.  149, 
150, 152, 183,  189,  192-198,  319 
Prosencephalon     (forebrain),    the 


Diencephalon  and  Telencepha- 
lon; sometimes  apphed  to  the 
Cerebral  hemispheres  onlv,  126- 
128,  130,  175 

Protista,  23 

Protopathic  sensibility,  a  primitive 
type  of  diffuse  cutaneous  sensi- 
bility, especiallv  on  hair-clad 
parts,  89,  90 

Protoplasm,  livina:  substance,   25, 
74,  102 
nervous,  39,  74,  102 

Protozoa,  one-celled  animals.  25, 
349 

Psalterium.     See  Lyre  of  David 

Pseudocoele.  See  Cavum  septi  pel- 
lucid! 

Psychogenesis,  the  development  of 
mind,  277,  285,  328.  339,  346- 
351 

Psychology,  general,  331 
physiological,  331 

Pulvinar,  a  visual  center  in  the 
thalamus,  164,  177,  179,  180, 
183.  184,  232.  236,  318,  341 

PuRKiNJE,  cells  of.  53,  54,  212,  213, 
214 

Purple,  visual,  231 

Putamen,  a  part  of  the  Nucleus 
lentiformis 

Pyramid  (pyramis),  an  eminence 
on  the  ventral  surface  of  the 
medulla  oblongata  produced  by 
the  pyramidal  tract  and  from 
which  the  latter  receives  its 
name,  123,  169 

Pvramids.  decussation  of,  142 

Pyramis,  209,  210,  211 

Pyriform  lobe.  See  Lobe,  pjrri- 
fonn 

QuAix,  14 

Quale,  a  quality  pertaining  to  any- 
thing; specifically  a  quality  of 
sensation  or  other  conscious 
process,  277,  289,  342,  344.  345 

Rabbit,  cortico-spinal  tract  of,  344 
development  of  eye  of,  228 
spinal  cord  of.  144 
Radiations,  sensory,  the  thalamo- 
cortical    tracts.     See     Tract, 
thalamo-cortical    and  Corona 
radiate,  321 


384 


INDEX   AND    GLOSSARY 


Radiations,  auditory,  185,  321 
gustatory,  321 

olfactory,     the     olfacto-cortical 
tracts;  the  term  has  also  been 
applied  to  various  subcortical 
olfactory  tracts,  321 
optic,  185,  234,  321 
soraesthetic  (of  tactile  and  gen- 
eral sensation),  321 
Radix.     See  Root 
Rage.     See  Anger 
Ram6n  y  Cajal,  S.,  14,  43,  45,  51, 
53,  54,  56,  58,  111,  212,  214,  238, 
264,  266,  267,  299-300,  310 
Ramus  communicans,  a  communi- 
cating branch  between  the  gan- 
glia of  the  sympathetic  Trunk 
and    the    roots    of    the    spinal 
nerves,  136,  137,  250,  254,  258 
Range  of  behavior,  19,  337 
Ranson,  S.  W.,  258,  260,  263,  276, 

281 
Raistvier,  node  of.     See  Node  of 

Ranvier 
Rat,  nervous  system  of,  244 
Rate  of  nervous  conduction,   103, 

104 
Rauber  and  Kopsch,  14 
Reaction,  a  change  in  bodily  state 
in  response  to  stimulation;  cf. 
Reflex,  70 
avoiding.     See  Reflex,  avoiding, 
of  degeneration,  317 
discriminative,  104,  286,  336,  342 
time,  the  time  required  for  re- 
sponse   to    stimulation,     104, 
286,  287 
Reading,       apparatus      of.      See 

Speech,  apparatus  of 
Receptor,  a  sense  organ,  26,  40,  74 
contact,  a  sense  organ  adapted  to 
respond  to  impressions  from 
objects   in   contact   with   the 
body ;  opposed  to  distance  Re- 
ceptor 
distance,  a  sense  organ  adapted 
to  respond  to  impressions  from 
objects  remote  from  the  body, 
23 
Recess,  epitympanic,  217 
infundibular,  127,  128 
lateral,  the  widest  part  of  the 
fourth  Ventricle  under  the  cere- 
bellum 


Recess,  optic,  the  depression  in  the 
lateral  wall  of  the  diencephalon 
formed  by  the  evagination  of 
the  optic  Vesicle,  126-128 
utricular.     See  Utricle 
Reflex  act,  a  simple  form  of  inva- 
riable Behavior  requiring  a 
nervous  system,  26,  32,  59, 
117 
time  of.     See  Reaction  time 
allied,  60,  61,  62,  64 
antagonistic,  60,  61,  62,  64 
arc.     See  Reflex  circuit 
avoiding,  280,  281,  287 
of  brain  stem,  198,  215,  311,  312, 

338,  339 
bulbar,  198,  311 
chain,  60,  61,  63,  64,  342 
circuit,  a  chain  of  neurons  which 
function  in  a  Reflex  act,  26, 43, 
59,  61,  63,  65,  66,  68-72,  117, 
121,  144,  145,  288,  342-345 
conditional,  269 
cortical,  320,  323 
cycHc,  64,  343 
discriminative.     See    Reaction, 

discriminative 
of  feeding;  cf.  Oral  sense,  245. 

311 
locomotor,  146 
of  medulla  oblongata,  198,  199, 

311 
myenteric,  268 

pattern,  69,  245,  339,  341,  346 
proprioceptive,  192-198 
of  spinal  cord,  140,  143-146,  191- 

199,  261,  311,  338,  339 
thalamic,  179,  182,  198,  281,  282, 
338,  340,  345 
Regeneration   of   nervous  tissues, 

50 
Region,  cortical,  a  group  of  related 

cortical  Areas,  304,  306 
Regulation,  the  process  of  adajjta- 
tion  of  form  or  behavior  of  an 
organism  to  changed  conditions, 
32 
Reid's  chart,  69,  148 
Reil,  island  of.    See  Insula 
Reinforcement,  62,  65,  66,  107,  214, 

243 
Reissner,      membrane      of.     See 

Membrane,  vestibular 
Reptiles,  cerebral  cortex  of,  240 


INDEX    AND    GLOSSAKY 


385 


Resistance,  nervous,  111,  28U,  280, 

329,  330,  338,  341 
Resolution,  physiological,  01,  327, 

338,  340,  341 
Respiratory    apparatus,    95,    15(), 

101,  257,'  201,  203-208 
Restiform  body.    See  Corpus  resti- 

forme 
Reticular  formation.     See  Forma- 

tio  reticularis 
Retina,  132,  100,  228,  230-232 

pigment  of  231,  232,  235 
Retraction  of  the  neuron,  110,  111 
Retzius,  G.,  90,  94,  135,  219,  220, 

243 
Reverberation,  cortical,  327,  330 
Rhinencephalon  (nose  brain),  the 
olfactory  part  of  the  brain,  119, 
120,  127,  128,  132,  239,  300 
Rhodopsin,  231 

Rhombencephalon,  that  part  of  the 
brain     below     the     Isthmus, 
including  the  Medulla  oblon- 
gata and  Cerebellum,  125-129, 
130-132,  155 
development  of,  125-128 
Rivers,  W.  H.  R.,  100,  101,  154 
Rod  of   CoRTi    (pillar  of   Corti), 
219,  221 
of  retina,  229,  230,  231,  235 
Rogers,  F.  T.,  182,  188  ^ 
Rolando,  fissure  of.         See  Sulcus 
centralis 
gelatinous    substance     of.     See 
Substantia  gelatinosa  Rolandi 
Root  (radix),  a  nerve  root,  or  the 
part  of  a  nerve  adjacent  to  the 
center  with  which  it   is  con- 
nected; in  the  case  of    spinal 
and  cranial  nerves,   the  part 
lying  between  the  cells  of  ori- 
gin   or    termination    and    the 
ganglion 
anterior.     See  Root,  ventral 
dorsal  (radix  dorsalis,  posterior 
root,  radix  posterior),  the  dor- 
sal or  sensory  Root  of  a  spinal 
or  cranial  nerve,  137,  139-141, 
144,  145,  147,  150,  164,  165, 
253,  254 
posterior.     See  Root,  dorsal 
spinal,  composition  of.  137,  146, 

147,  161,  164,  165 
ventral    (radix  ventralis,    radix 
25 


anterior),   the  ventral  or  iiiolor 
root  of  a  spinal  or  cranial  ncrvr, 
137,  139-141,  144,  145,  164,  165, 
199,  253 
Rostral,  pertaining  to  the  beak  or 
snout,    or   directed   toward   the 
front  end  of  the  body  as  opposed 
to  Caudal 
Rostrum  of  corpus  callosum,  128 
Russell,  J.  S.  Risien,  210 
Rynberk,  G.  Van,  208,  209,  210 


Sabin,  Florence  R.,  109 
Sac,  dorsal  (saccus  dorsalis),  a  dor- 
sal   evagination    of    the    Tela 
chorioidea  of  the  third  ventri- 
cle in  .some  vertebrate  brains 

endolymphatic  (saccus  endolym- 
phaticus),  218 

nasal,  118,  119 
Saccule    (sacculus),    part    of    the 

membranous    labyrinth    of    the 

ear,  92,  201,  217,  218,  222,  223 
Sachs,  E.,  188 
Sala,  C.  L.,  85 
Saliva,     secretion     of.     See     also 

Gland,  salivarv,    100,    101,  2e9i 

274 
Sarcophaga  carnaria,  nervous  svs- 

tem  of,  31 
Scala    media.     See    Ductus    coch- 
learis 

tympani,  219 

vestibuli,  219 
Scarp.\,    ganglion    of.     See    Gan- 
glion, vestibular 
Schaefer,  E.  a.,  14,  238 
Schaper,  a.,  210 

SciiHNEMANN,   A.,  226 

ScHULTZE,  tract  of  (comma  tract) 
See  Fasciculus  interfascicularis 

ScHWALBE,  vestibular  nucleus  of, 
202,  203 

Schwann,  sheath  of.     See  Neuri- 
lemma 

Scyllium,  nervous  system  of,  118 

Sea-robin,  nervous  svstem  of,  165, 
167 

Secretin,  249 

Secretions,    effect   of   fatigue   and 
emotion  on,  109,  283 
internal,  179,  249,  258,  283,  284 
psychic,  269 


386 


INDEX    AND    GLOSSARY 


Segment,    mesodermal,    or    primi- 
tive.    See  Somites 
Segmental    apparatus,    the    Brain 

stem,  122,  123,  132 
Segmentation  of  nervous  system, 

29,  30,  31,  122,  136,  156,  164 
Self-consciousness,  349 
Senility,  350 
Semicircular  canals,  nerve  endings 

in,  93,  94 
Semon,  R.,  329 

Sensation,    a    subjective    process 
arising  in  response  to  stimula- 
tion,  75,   116,   277,   278.    285, 
288,  289 
common,  288 
in  lower  animals,  77 
neurological  mechanism  of,  285, 

289 
visceral,  81,  94-97,  162,  253-256, 
261-274,  278,  288 
Sense,  criteria  of,  79 

organ.     See  Receptor 
Sentiments.     See  Affection 
Septum,   the "  medial   wall   of   the 
cerebral   hemisphere   between 
the  Lamina  terminalis  and  the 
olfactory  Bulb ;  in  man  its  up- 
per part  is  thin  and  forms  the 
Septum  pellucidum,  244,   341 
dorsal  median,  of  cord.     See  Fis- 
sure, dorsal 
pellucidum,  a  thin  sheet  of  nerv- 
ous tissue  forming  a  portion  of 
the  medial  wall  of  each  cere- 
bral hemisphere  between  the 
Corpus  callosum  and  the  For- 
nix, 177 
Sexual  organs,  innervation  of,  257 

sensations  from,  95 
Shambaugh,  G.  E.,  220,  226,  227 
Shark,    nervous    system    of.     See 

Fishes,  nervous  system  of 
Sheath,    medullary.     See    Myelin 
sheath 
myelin.     See  Myelin  sheath 
primitive.     See  Neurilemma 
of  Schwann.     See  Neurilemma 
Sheldon,  R.  E.,  14,  101,  174,  188, 

276 
Shepard,  John  F.,  110,  113 
Sherren,  J.,  100,  154 
Sherrington,  C.  S.,  36,  38,  69,  73, 
80,  82,  101,  135,  146,  154,  189, 


197,  216,  270,  278,  288,  289,  291, 
314,  315,  316,  317,  333,  334 

Shock,  spinal,  the  transient  or  per- 
manent loss  of  spinal  reflexes 
after  severing  the  spinal  cord 
from  the  brain,  68 

Shoemaker,  D.  M.,  134 

Sight,  organs  of.  See  Visual 
apparatus 

Sinus,  inferior,  of  labyrinth,  218 

Skin  brain,  121,  132 

•Skin,  nerves   of.     See  Nerves,  cu- 
taneous 
nerve-endings  in,  84-91,  273,  281 
sensibility  of,  75,  77,  84-91,  143, 
189-198,    236,    253-255,    273, 
277-281,  289 

Sleep,  110,  331 

Smell,  organs  of.  See  Olfactory 
apparatus 

Smith,  G.  Elliot,  208-211,  216, 
293,  307,  310 

Sneeze,  mechanism  of,  266 

Social  evolution,  349,  350 

Somatic  area.     See  Area,  somatic 
cortex.     See  Neopallium 
nerves.     See  Nerve,  somatic 
organs,  those  concerned  with  the 
adjustment  of  the  body  to  its 
environment,  81,  84,  98,  189 

Somesthetic  apparatus,  the  general 
somatic  sensory  systems,  includ- 
ing cutaneous  and  deep  sensibil- 
ity, 178,  181,  189-198 

Somites  (myotoms,  primitive  seg- 
ments, mesodermal  segments), 
segmented  masses  of  mesoderm 
in  vertebrate  embryos  which  give 
rise  to   the  somatic  museles,  98 

Sound,  reaction  time  to,  104 

receptors  for.     See  Auditory  ap- 
paratus 

Space,  discrimination  of,  141,  189, 
195,  196 
perforated.     See  Substantia  per- 
forata 
subarachnoid,  133 

Speech,  apparatus  of  (including 
reading  and  writing) ;  cf .  Apha- 
sia, 316,  325-327 

Spencer,  Herbert,  17 

Sphere,  cortical.  See  Center,  cor- 
tical 

Spiders,  nervous  system  of,  30 


INDEX    AND    GLOSSARY 


387 


Spielmeyer,  W.,  316 
8PILLER,  W.  G.,  192,  198 
Spinal  animal,  U8 
cord    (medulla    spinalis),     that 
portion  of  the  central  nerv- 
ous system  contained  witliin 
the    spinal     Canal    of     the 
spinal    column,     114,     115, 
127,  128,  136-153,  164,  165, 
199 
cervical,  140,  141 
development  of,  199 
functions  of,  68,  140,  143,  261, 

264,  279-281,  345 
lesions  of,  189,  195-197,  264, 

279 
tracts  of,  141,  150,  152,  190, 
194 
shock.     See  Shock,  spinal 
Spiracle,  a  rudimentary  gill  cleft  in 
some  fishes,  represented  in  mam- 
mals by  the  auditory  or  Eusta- 
chean  tube,  118,  119,  120 
Spitzka,  E.  C,  116 
Splanchnic,  visceral,  81 
Spongioblast,  one  of  the  epithehal 
cells   of   the  embryonic    Neural 
tube  which  becomes  transformed 
into  an  Ependyma  cell 
Spurzheim,  J.  K.,  312,  313 
Stabler,  Eleanor  M.,  80,  101 
Stalk,  optic,  228 
Steiner,  J.,  146,  154 
Stem.     See  Brain  stem 
Stewart,  G.  N.,  284 
Stiles,  P.  G.,  13,  108,  113,  276 
Stilling,  dorsal  nucleus  of.     See 

Nucleus,  dorsal,  of  Clarke 
Stimulus,  a  force  which  excites  an 
organ  to  activitv,  59,  74 
adequate,  26,  39,  74,  81 
Stomach,  156,  161,  249,  261,  267, 

268-270 
Streeter,  G.  L.,  169,  227 
Stria  acustica.     See  Stria  medul- 
laris  acustica 
of    Baillar(;eu.     See    Line    of 

Baillarger 
of  Gennahi.     Sec  Line  of  Gen- 

nari 
longitudinalis  (stria  of  Lancisi, 
nerve  of  LancisO,  slender  bun- 
dles   of    nerve-fibers    running 
along  the  dorsal  surface  of  the 


Corpus  callosum  in  the  floor  of 
the  longitudinal  fissure 
meduUaris    acustica,    secondary 
acoustic  fibers  arising  in  the 
dorsal  cochlear  nucleus  and 
decussating  across  the  floor 
of  the   fourth   ventricle   to 
reach    the   opposite   lateral 
Lemniscus,  224 
thalami,  a   band  of  fibers  ac- 
companying the  Taenia  thai- 
ami  along  the  dorsal  border 
of  the  thalamus,  containing 
the  tractus  olfacto-habenu- 
laris,    tractus    cortico-habe- 
nularis,    and    other    fibers, 
177,  180,  181,  183,  244 
olfactoria    intermedia,     a     sec- 
ondary olfactory  Tract  from 
the  olfactory  Bulb  to  the  Tu- 
berculum  olfactorium,  most 
of  its  fibers  first  crossing  in 
the    anterior    Commissure, 
243 
lateralis,  a  secondary  olfactory 
Tract    from    the     olfactory 
Bulb  to  the  Nucleus  olfac- 
torius  lateralis,  243 
medialis,   a   secondary    olfac- 
tory Tract  from  the  olfac- 
tory Bulb  to  the  Nucleus  ol- 
factorius  medialis,  243 
semicircularis.     See  Stria  termi- 

nalis 
terminalis    (stria   semicircularis, 
old  term,  taenia  semicircularis), 
a  correlation  tract  between  the 
Nucleus  amygdalae  of  the  lat- 
eral  olfactory   Area   and   the 
medial    olfactory    Area,    123, 
177,  296 
vascularis  of  cochlea,  219 
Striate  area.     See  Area  striata 
liody.     See  Corpus  striatum 
Stricht,  van  der,  O.,  219-221,  227 
Stripe  of   Baillarger.     See  Line 
of  Baillarger 
of  Genn.vri.     See  Line  of  Gen- 

nari 
of  Hensen,  221 
Strong,  O.  S.,  207,  210 
Strongman,  B.  T.,  58 
Sturgeon,  nervous  svsteni  of,   165, 
166 


388 


INDEX    AND    GLOSSARY 


Subconscious   mind.     See    Uncon- 
scious cerebration 
Subiculum,  that  part  of  the  Gyrus 
hippocampi    which    borders    the 
fissura    hippocampi;    sometimes 
applied    to    the    whole    of    this 
gyrus,  246 
Substance,  black.     See  Substantia 
nigra 
chromophilic   (Nis.sl  substance, 
tigroid  substance,  or  bodies,  or 
granules),  a  proteid  substance 
typically  present  in  the  cyto- 
plasm of  nerve-cells,  41,  42,  43, 
47,  48,  50,  51,  105,  108,  148, 
316 
gray.     See  Matter,  gray 
perforated.     See  Substantia  per- 
forata 
white.     See  Matter,  white 
Substantia    alba.     See    Matter, 
white 
gelatinosa    Rolandi    (gelatinous 
substance    of    Rolando),    an 
area  of  Neuropil  bordering  the 
dorsal    gray    column    of    the 
spinal    cord;    sometimes    also 
applied  to  the  nucleus  of  the 
spinal  V  tract  in  the  medulla 
oblongata,  140,  266 
grisea.     See  Matter,  gray 
nigra  (black  substance),  an  area 
of   gray    matter    immediately 
dorsal  of  the  Basis  pedunculi, 
functionally  related  to  the  cor- 
tico-pontile  tracts,    176,    180, 
183,  234 
perforata,  anterior  (anterior  per- 
forated substance  or  space), 
a  region  on  the  ventral  sur- 
face of  the  brain  in  front  of 
the  optic  Chiasma  which  is 
pierced  by  many  small  arte- 
ries, 129,  243,  341 
posterior  (posterior  perforated 
substance  or  space),   a  re- 
gion on  the  ventral  surface  of 
the  brain  between  the  Bases 
pedunculi  which  is  pierced 
by  small  arteries,  129 
Subthalamus,  the  ventral  part  of 
the    Thalamus,    179,    180,    181, 
183,  190,  194,  341 
Sulcus,  in  the  cerebral  cortex,   a 


superficial  fold  not  involving 
the  entire  thickness  of  the 
brain  wall;  cf.  Fissure,  295 

anterior  parolfactory,  128 

central  (fissure  of  Rolando,  cru- 
ciate sulcus),  128,  130,  314, 
315 

cinguli,  128 

corporis  callosi,  128 

cruciate.     See  Sulcus,  central 

frontalis,  inferior,  130 
superior,  130 

horizontalis,  210 
magnus,  211 

interparietalis,  130 

limiting  (sulcus  limitans),  a  lon- 
gitudinal groove  on  the  ven- 
tricular surface  of  the  embry- 
onic brain  separating  the  dor- 
so-lateral  sensory  Plate  from 
the  ventro-lateral  motor  Plate, 
37,  126,  129,  167,  198 

occipitalis  transversus,  130 

postcentralis,  211 

postclivalis,  211 

posterior  parolfactory,  128,  243 

postpyramidalis,  211 

precentralis,  130 
cerebelli,  211 

primarius,  210,  211 

rhinalis.     See  Fovea  limbica 

spiralis,  219,  220,  221 

uvulo-nodularis,  211 
Summation,  central.     See  Conduc- 
tion,   avalanche,    and    Rein- 
forcement 

of  stimuli,  the  enhancement  of 

effect  by  repeated  stimulation, 

62,  65,  66,  214,  232,  242,  286, 

289,  301,  341 

Suprasegmental     apparatus,     the 

cerebral   cortex  and   cerebellum 

with  their  immediate  dependen- 
cies, 122,  132,  155,  173,  204 
Susceptibility  of  neurones  to  pois- 
ons, 103,  256 
Swallowing,  apparatus  of,  83,  274 
Sylvius,  aqueduct  of.     See  Aque- 
duct of  Sylvius 

fissure  of.     See  Fissure,  lateral 

fossa  of.     See  Fossa  lateralis 
Symbolizing,  defects  of,  325 
Sympathetic  nervous  system.     See 

Nervous  system,  sympathetic 


INDEX    AND    GLOSSARY 


380 


Synapse,  the  place  where  the  nerv- 
ous   impulse    is    transmitted 
from  one  neuron  to  another, 
52-57,  103,  108,  117,  242,  301, 
329 
fatigue  of,  108,  111 
time  of  transmission  through,  57, 
105 
Synergic    muscles.     See    Muscles, 

synergic 
System,  functional,  all  neurons  of 
common  physiological  type. 
Most  peripheral  nerves  contain 
several  components  belonging  to 
different  systems,  157-170 

Tabanus  bovinus,  nervous  system 

of,  31 
Taenia,  the  line  of  attachment  of  a 
membranous  part  to  a  massive 
part  of  the  brain  wall ;  formerly 
applied  also  to  some  fiber 
tracts,  as  Taenia  semicircularis 
=  Stria  terminalis,  and  Taenia 
thalami  =  Stria  meduUaris 
thalami 

chorioidea,  the  line  of  attach- 
ment of  the  lateral  choroid 
Plexus  to  the  medial  wall  of  the 
cerebral  hemisphere.  (This 
portion  of  the  medial  wall  is 
adherent  to  the  thalamus, 
forming  the  Lamina  affixa) 
Taenia  fornicis,  the  line  of  attach- 
ment of  the  lateral  choroid 
Plexus  to  the  Fimbria  of  the 
Fornix 

thalami,  the  line  of  attachment 
of  the  Tela  chorioidea  of  the 
third  ventricle  to  the  dorsal 
margin  of  the  thalamus.  _  This 
name  was  formerly  applied  to 
a  band  of  fibers,  the  Stria 
meduUaris  thalami,  which  bor- 
ders the  taenia,  177 

.ventriculi  quarti,  the  line  of  at- 
tachment of  the  membranous 
roof  of  the  fourth  ventricle  to 
the  medulla  oblongata,  169 
Tashiro,  S.,  103,  113 
Taste,  apparatus  of.     Sec  Gusta- 
torv  apparatus 
bud,  "96,  1515,  242,  270-274 


Taste,  peripheral  nerves  of.     See 

Nerves,  gustatory 
Taxis.     See  Tropism 
Tectum  mesencephali,  the  roof  of 
the  midbrain,  comprising  the 
Colliculus     superior     (tectum 
opticum)    and   the    Colliculus 
inferior,  176 
optic.     See  Colliculus,  superior 
Teeth,  90,  161,  277 

of  HUSCHKE,   221 

Tegmen  ventriculi  quarti,  the  roof 
of  the  fourth  ventricle,  formed 
chiefly  by  the  Velum  medullare 
anterius,  the  Velum  medullare 
posterius,  and  the  Plexus  chori- 
oideus  ventriculi  quarti 
Tegmentum,  the  dorsal  part  of  the 
cerebral  Peduncle  between  the 
Basis  pedunculi  and  the  Aque- 
duct of  Sylvuis;  often  described 
as  also  extending  backward  into 
the   corresponding   part   of   the 
medulla  oblongata,  172,  199 
Tela,  any  thin  non-nervous  part  of 
the  brain  wall 
chorioidea,  that  portion  of  the 
Pia  mater  which  covers  any 
thin  non-nervous  part  of  the 
brain  wall,  including  the  chor- 
oid Plexuses,  133 
Telencephalon  (endbrain),  the  an- 
terior  end   of   the   embryonic 
Neural  tube  and  its  adult  de- 
rivatives,   comprising    chiefly 
the  cerebral  hemispheres  and 
Lamina    terminalis,    126-128, 
130,  132,  175 
medium,  that  portion  of  the  em- 
bryonic Telencephalon  which 
is  not  evaginated  to  form  the 
cerebral  hemispheres;  it  com- 
prises chiefly  the  Lamina  ter- 
minalis and  Pars  optica  hypo- 
thalami, 130 
Telodendron.thc  tcrmmal  branched 
end  of   a    Dendrite;  sometimes 
applied  also  to  that  of  an  Axon; 
cf.  Terminal  arborization 
Temperature,  apparatus  of,  76,  90, 
143,  149-152,  181,  189-196,  269, 
282,  289 
Tendon,  nerve  endings  m,  93 
sense,  82,  93,  143 


390 


INDEX   AND    GLOSSARY 


Tentorium  cerebelli,  a  transverse 
fold  of  Dura  mater  between  the 
cerebellum  and  the  cerebral  hem- 
ispheres, 133 

Terminal  arborization,  the 
branched  end  of  an  axon;  some- 
times applied  also  to  that  of  a 
Dendrite,  41 

Terminology.  See  Nervous  sys- 
tem, terminology  of 

Testes.     See  CoUiculus,  inferior 

Thalamencephalon.  See  Dien- 
cephalon 

Thalamus,  the  middle  and  larger 
subdivision  of  the  Dienceph- 
alon,  sometimes  applied  to  the 
entire  diencephalon  and  called 
Thalamus    opticus,    66,    120, 
123,  126,   130-132,   152,   177- 
183,   191,   194,  228,   281-283, 
234,  311,  345 
lesions  of,  281-283,  311 
new.         See  Neothalamus 
old.     See  Palseothalamus 
opticus.     See  Thalamus 
pain  center  in,  182,  281-283,  288, 

345 
respiratory  center  in,  266 

Thirst,  apparatus  of,  95 

Thompson,  T.,  154,  192,  196,  291 

Thorns  of  dendrites,  303 

Threshold,  the  minimal  stimulus 
which  will  excite  an  organ  to  ac- 
tivity, 77,  86,  97,  143,  189,  242, 
281-283 

Tickle,  81,  282 

Tigroid  "bodies,  substance,  or  gran- 
ules. See  Substance,  chromoph- 
ilic 

Time,  central.     See  Pause,  central 
latent.     See  Pause,  central 
reaction.     See  Reaction  time 

Tissue,  the  cellular  fabric  of  which 
the  body  is  composed,  25 

TiTCHENER,  E.  B.,  75 

ToLDT,  Carl,  14 

Tone,  affective.     See  Feeling  tone 
and  Affection 
analysis,  220,  222,  224 
feeling.     See   Feeling   tone   and 

Affection 
muscular,  82,  93,  207,  214 
nervous,  107,  214,  333 

Tongue,  muscles  of,  98, 156, 159, 161 


Tongue,  nerves  of,  156,    160-162, 

272  273 
Tonsilla'  209,  210 
Touch,  apparatus  of,  65,  75,  84r-90, 
143,   150,   151,   152,   179-182, 
269,  270,  273,  280,  281,  285 
reaction  time  of,  104 
Toxines.     See  Poisons 
TozER,  F.  M.,  197 
Tract    (tractus),    a    collection    of 
nerve-fibers  of  like  origin,  ter- 
mination,   and    function;    cf. 
Fasciculus,  28,  106,  139,  338 
association;  cf.   Fibers,  associa- 
tion, 61,  67,  296,  319 
bulbo-spinal,  171 
central  tegmental,  205 
cerebello-tegmental,  205 
comma.     See    Fasciculus   inter- 

fascicularis 
cortico-bulbar,    176,    184,    186, 

198,  317 
cortico-cerebellar.     See    Tract, 

cortico-pontile 
cortico-mesencephalic,  321 
cortico-oculomotor,  184 
cortico-pontile,    176,    184,    186, 

205,  206,  207,  323 
cortico-rubral,  170,  185,  323 
cortico -spinal     (fasciculus    cere- 
bro-spinalis,  B.  N.  A.,  pyra- 
midal tract),  the  voluntary 
motor  path  from  the  precen- 
tral  gyrus  of  the  cerebral  cor- 
tex to  the  spinal  cord,  where 
it  divides   into    lateral  and 
ventral  parts,   71,   139,  141, 
142,  151,  152,  169,  170,  176, 
183,     184,     186,    198,    205, 
214,  315-318,  321,  344,  345 
lateral      (fasciculus     cerebro- 
spinalis  lateralis,  B.  N.  A., 
lateral  or  crossed  pyramidal 
tract),  141,  142,  152 
ventral     (fasciculus    cerebro- 
spinalis  anterior,  B.  N.  A., 
ventral  or  direct  pyramidal 
tract,    column   of    TtJRCK), 
141,  142,  152 
cortico-thalamic,  323 
direct    cerebellar.     See  Tract, 

spino-cerebellar,  dorsal 
of  Flechsig.     See  Tract,  spino- 
cerebellar, dorsal 


INDEX    AND    GLOSSARY 


391 


Tract.  ofGowERs.  See  Fasciculus 
ventro-lateralis  superficialis 

habenulo-podunculai-  (fasciculus 
retroflexus,  Meynert's  bun- 
dle), 180,  244 

of  Helavig.  Sec  Tract,  olivo- 
spinal 

internuncial,  a  fiber  tract  con- 
necting two  nuclei  or  centers, 
69 

of  LissAUER.  See  Fasciculus 
dorso-lateralis 

of  LowENTHAL.  See  Tract,  tec- 
to-spinal 

mamillo-peduncular,  176,  244 

mamillo -thalamic  (fasciculus 
thalamo-mamillaris  B.  N.  A., 
tract  of  Vicqd'Azyr),  180,  244 

mesencephalic,  of  V  nerve,  176 

of  Meynert.  See  Tract,  haben- 
ulo-peduncular 

of  MoNAKOw.  See  Tract,  rubro- 
spinal 

nomenclature  of,  139 

olfactory  (tractus  olfactorius),  ol- 
factory fibers  of  the  second 
order  passing  from  the  olfac- 
tory Bulb  to  the  nuclei  of  the 
Area  olfactoria.  See  Stria  ol- 
factoria,  123,  129,  180,  242, 
243,  244 

olfacto-hypothalamic,  244 

olfacto-tegmental,  244,  245 

olivo-cerebellar,  169,  194,  205, 
207 

olivo-spinal  (Helwig's  bundle, 
tractus  triangularis),  141,  142 

optic  (tractus  opticus),  that  por- 
tion of  the  optic  path  which 
passes  between  the  optic  Chi- 
asma  and  the  optic  centers  in 
the  thalamus  and  midbrain. 
(The  term  might  properly  be 
extended  to  include  also  the 
so-called  optic  Nerve),  123, 
129,  176,  181,  183,  232,  233, 
234 

ponto-cerebellar,  205 

predorsal.  See  Tract,  tecto- 
spinal 

projection.    See  Projection  fibers 

pyramidal.  See  Tract,  cortico- 
spinal 

respiratory,  264,  265,  266 


'I'ract,    rubro-spinal    (Mo.nakow's 
tract),  141,  142,  170,  176,  205, 
207 
rubro-thalamic,  205 
of  Schultze.     See  Fasciculus  in- 

tcrfascicularis 
secondary  gustatory.     See  Lem- 
niscus, visceral 
visceral.     See  Lemniscus,  vis- 
ceral 
septo-marginal,  141,  142 
solitario-spinalis,  264,  266,  267 
solitary.     See    Fasciculus    soli- 

tarius 
of  spinal  cord.     See  Spinal  cord, 

tracts  of 
spinal,  of  V  nerve,  162,  163,  167, 
168,  169,  170,  191,  197 
of  vestibular  nerve,  169 
spino-cerebellar,    123,    139,    149, 
197 
dorsal     (fasciculus    cerebello- 
spinalis,     B.  N.  A.,    direct 
cerebellar  tract,  Flechsig's 
tract),   141,   150,   170,   194, 
205,  207 
ventral  (part  of  Gowers'  fas- 
ciculus,   or    Fasciculus    an- 
terolateralis  superficialis,  B. 
N.  A.),  141,  150,  170,  194, 
205 
spino-olivary,  141,  142,  194,  205 
spino-tectal,  141,  142,  176,  197 
spino-thalamic,  lateral,  141,  142, 
150,  197 
ventral,  141,  142,  150 
tecto-cerebellar,  194,  205 
tecto-spinal    (predorsal    bundle, 
tract    of    Lowenthal),     141, 
143,  153,  170,  235 
terminology  of,  139 
thalamo-bulbar,  198 
thalamo-cortical;  cf.   Projection 
fibers    and    Radiations,    178, 
184,  190,  194,  321,  340 
thalamo-olivary,  176 
thalamo-peduncular,  180 
thalamo-spinal,  198 
triangular.     See     Tract,     olivo- 
spinal 
vestibulo-cerebellar,     171,     194, 

203,  207 
vcstibulo-spiual,    141,    143,    153, 
171,  194,  203 


392 


INDEX   AND    GLOSSARY 


Tract  of  ViCQ  d'Azyr.     See  Tract, 

mamillo-thalamic 
Transmission  of  nervous  impulse. 

See  Conduction,  nervous 
Trapezoid  body.     See  Body,  trape- 
zoid 
Trigonum  habenulae,  a  triangular 
area  at  the  posterior  end  of  the 
Habenula,  177 
hypoglossi      (eminentia      hypo- 
glossi),  a  ridge  in  the  floor  of 
the  fourth  ventricle  produced 
by  the  XII  nucleus,  168,  170 
olfactorium,  a  triangular  expan- 
sion of  the  Crus  olfactorium 
from  which  the   Striae    olfac- 
torise  arise 
vagi.     See  Ala  cinerea 
Tropism,  a  simple  form  of  invari- 
able   behavior  not  requiring   a 
nervous  svstem,  60 
Trotter,  W.,  90,  101,  189 
Trunk  (truncus),  the  main  stem  of 
a     nerve     from     which     the 
branches  (rami)  are  given  off. 
See  Nerve 
sympathetic  (ganglionated  sym- 
pathetic    cord,     sympathetic 
chain,   vertebral  sympathetic 
chain),    a    strand    of    sympa- 
thetic nerves  and  ganglia  ex- 
tending along  each  side  of  the 
vertebral    column,    115,    250, 
251 
Tube,  auditory  (Eustachean  tube), 
217 
neural.     See  Neural  tube 
Tuber  cinereum,  a  gray  eminence 
forming  the  ventral  part  of  the 
Hypothalamus,  123,  128,  129, 
179,  183,  341 
vermis,  209,  210,  211 
Tubercle,  anterior,  of  thalamus,  an 
eminence  on  the  dorsal  surface 
formed  by  the  Nucleus  anterior 
thalami,  177 
Tuberculum    acusticum    of    fishes 
(part  of  the  Area  acustico- 
lateralis),  162,  163,  166,  223, 
of  mammals  (the  dorsal  coch- 
lear nucleus),  224 
cinereum,  an  eminence  on  the 
lateral  aspect  of  the  medulla 
oblongata  produced  chiefly  by 


the  spinal  V  tract  and  its  nu- 
cleus 
cuneatum,  an  eminence  on  the 
dorsal  surface  of  the  lower  end 
of  the  medulla  oblongata  later- 
ally of  the  Clava  produced  by 
the  nucleus  of  the  Fasciculus 
cuneatus,  141,  152,  194,  205 
fasciae  dentatse,  244 
olfactorium  (lobus  parolfactorius 
of  Edinger),  the  intermediate 
olfactory  Nucleus,  lying  in  the 
Substantia  perforata  anterior; 
cf.  Area  olfactoria,  243,  244, 
306 
Tunnel  of  Corti,  219,  221 
TtJRCK,  column  of,  the  ventral  cor- 

tico-spinal  Tract 
Turner,  W.  A.,  216 
Tympanic  membrane.  Tympanum 
See  Membrane,  tympanic 


Unconscious  cerebration,  330,  331, 
343   345 
mind,'330,  331,  343 

Unconsciousness,  331 

Uncus,  the  hook-shaped  extremity 
of  the  Gyrus  hippocampi,  part  of 
the  Archipallium,  243,  306 

Unpleasantness.     See  Affection 

Utricle  (utriculus,  recessus  utric- 
uli),  part  of  the  membranous 
labyrinth  of  the  inner  ear,  92, 
201,  217,  218,  222,  223 

Uvula,  209,  210,  211 


Valve  of  ViEussENS.  See  Velum 
meduUare  anterius 

Valvula  cerebelli.  See  Velum  med- 
uUare anterius 

Van  der  Stricht,  O.,  219-221,  227 

Van  Gehuchten,  A.,  26,  46,  91, 
216 

Variable  behavior.  See  Behavior, 
variable 

Variation,  negative,  in  nerve-fibers, 
102 

Varoli  (Varolius).  See  Pons 
Varolii 

Vas  spirale  (spiral  vessel),  221 

Vasomotor  apparatus,  the  neuro- 
muscular mechanism  which  con- 


INDEX    AND    (iJ.OSSA'KY 


'.VXi 


trols  the  amount  of  blood  sup- 
plied to  any  part,  110,  257,  261, 
262 
Veins,  nerves  of.     See  Vasomotor 

apparatus 

Velocity    of    nervous    conduction. 

See  Nervous  impulse,  velocity  of 

Velum  anticum.     See  Velum  med- 

uUare  anterius 

interpositum,  the  Tela  chorioidea 

of  the  third  ventricle 
medullare  anterius  (or  superius), 
a  thin  portion  of  the  brain 
wall  containing  a  few  mye- 
linated  fibers  which  forms 
the  roof  of  the  fourth  ven- 
tricle in  front  of  the  cere- 
bellum, 128,  168,  211 
posterius,  a  thin  portion  of  the 
brain  wall  containing  a  few 
myelinated      fibers      which 
forms  a  small  part  of  the 
roof  of  the  fourth  ventricle 
immediately      behind      the 
cerebellum 
superius.     See  Velum  medul- 
lare anterius 
transversum,  a  transverse  fold  of 
the    Tela     chorioidea    which 
marks  the  boundary  between 
the  Diencephalon  and  the  Tel- 
encephalon in  the  embryonic 
brain 
Ventral,  on  the  front  or  belly  side 
of  the  body,  termed  Anterior  in 
the  B.  N.  A.  hsts,  125 
Ventricle,  a  cavity  within  the  brain 
and  spinal  cord  derived  from 
the  lumen  of  the  embryonic 
Neural  tube 
fifth.     See  Cavum  septi  pellucidi 
first.     See  Ventricle,  lateral 
fourth  (ventriculus  quartus,  met- 
acoele),    the   ventricle   of   the 
medulla  oblongata,   128,  130, 
166,  168,  293 
lateral  (paracoele),  the  ventricle 
of  each  cerebral  hemisphere; 
these  are  also  called  first  and 
second    ventricles,    130,    181, 
184,  293 
second.     See  Ventricle,  lateral 
third    (ventriculus   tertius,    dia- 
coele),  the  ventricle  of  the  di- 


encephalon, 130,  177, 184,  293, 
294 
Veratti,  E.,  52 

Vermis  cerebelli  (worm),  the  mid- 
dle lobe  of  the  cerebellum,  128, 
208,  209,  211,  213,  224 
Vertebrates,  behavior  of,  34 

nervous  svstem  of,  30 
Verworn,  M.,  38,  107 
Vesicle,  ciliated  olfactory,  the  spe- 
cific olfactory  receptive  organ, 
97 
optic,  an  outgrowth  from  the  lat- 
eral wall  of  the  diencephalon 
which  forms  the  nervous  part 
of    the    eyeball.     It    first    as- 
sumes the  form  of  a   simple 
hollow  sphere,  the  primary  op- 
tic   vesicle,    which    later    col- 
lapses to  form  a  two-layered 
optic  cup,  or  secondary  optic 
vesicle,  125,  126,  228 
Vessels,  lymphatic,  of  brain,  133 
Vestibular  apparatus,  93,  94,  118, 
119,  159,  161,  164,  201-204,  218, 
222,  223,  224 
Vestiges,  memory,  in  cortex,  329- 

331,  338,  341 
Vibrations,  table  of,  77 
Vibrissae,  innervation  of,  86,  87 
Vicarious  function  in  cortex,  328 
ViCQ  d'Azyr,  tract  of.     See  Tract, 

mamillo-thalamic 
Villiger,  E.,  14 

Vincent,  Stella  B.,  87,  101,  238 
Viscera,  the  internal  organs,  espe- 
cially those  concerned  with  the 
internal  adjustments  of  the  body, 
81,  93,  98,  156,  261-270,  278 
Visceral  apparatus,   182,  249-275, 
278,  288 
nerves.     See  Nerve,  visceral 
brain,  121,  132 
Vision,  stereoscopic,  233,  234 
Visual  apparatus,   65,  66,  76,  92, 
118-120,  132,  159,  160,  164,  178, 
180,  181,  183,  184,  204,  228-237, 
297,  311 
VoGT,  ().,  307,  310,  321 
Voluntary    movement,    apparatus 
of,  83,"  182,   198,  214,  268,  311, 
317,  319 
Vomiting,     mechanism     of,     267, 
270 


394 


INDEX    AND    GLOSSARY 


Waldeyer,  W.,  51,  58 

Warmth,  sensations  of.  See  Tem- 
perature, apparatus  of 

Washburn,  A.  L.,  275 

Washburn,  Margaret  F.,  38 

Watson,  J'.  B.,  38,  101,  227,  238, 
291 

Weed,  Lewis  H.,  133,  135,  169 

Weigert,  method  of,  140,  302 

Weight  of  brain,  132 

WiLLEMS,  E.,  197 

Willis,  circle  of.  See  Circle  of 
Willis 

Wilson,  J.  G.,  91,  101,  216,  272, 
276 

WooDwoRTH,  R.  S.,  104,  113,  238 

Word-blindness  (Alexia),  326 

Word-deafness,  326 

Worm.     See  Vermis  cerebelli 


Worms,  nervous  system  of,  29,  30, 

252 
Wrisberg,  nerve  of.     See  Nerve, 

intermediate 
Writing,  apparatus  of.    See  Speech, 

apparatus  of 
WUNDT,  W.,  104 

Yerkes,  R.  M.,  34,  38,  66,  73 

Zone,  cortical.     See  Center,  corti- 
cal 
dentate,  221 
of     Lissauer.     Sec     Fasciculus 

dor  so -lateralis 
of  neural  tube.     See  Plate 
papillary,  221 
Zwaardemaker,  H.,  248 


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M.  D.,  Professor  of  Physical  Education,  University  of  Pennsyl- 
vania. Octavo  of  585  pages,  with  478  illustratiwis.  Cloth,  I4.00 
net.  New  {2d)  Edition— Published  June,  igis- 

Chapters  of  special  value  in  college  work  are  those  on  exercise  by  the 
different  systems:  play-grounds,  physical  education  in  school,  college, 
and  university. 

D.  A.  Sargent,  M.  D.,  Hcmenway  Gymnasium:  "It  should  be  in  the 
hands  of  every  physical  educator." 


Saunders'  College  Text-Books 


B^iJickainiairii  &  iivji^irirayi  in)s^c^(Bwm\ 


Veterinary  Bacleriologv  By  Robert  E.  Buchanan,  Ph.  D.,  Pro- 
fessor of  Bacteriology,  and  Charles  Murray,  B.  Sc,  D.  V.  M., 
Associate  Professor  of  Veterinary  Bacteriology,  Iowa  State  College 
of  .'\griculture  and  Mechanic  Arts.  Octavo  of  500  pages,  illustrated. 
Cloth,  $3.50  net.       New  {2d)  Ediiion  — Published  Seplember,  iQt6. 

Professor  Buchanan's  new  work  goes  minutely  into  the  consideration 
of  immunity,  opsonic  index,  reproduction,  sterilization,  antiseptics, 
biochemic  tests,  culture  media,  isolation  of  cultures,  the  manufacture 
of  the  various  toxins,  antitoxins,  tuberculins,  and  vaccines. 
B.  F.  Kaupp,  D.  V.  S.,  State  Agricultural  College,  Fort  Collins:  "It  is 
the  best  in  print  on  the  subject.  What  pleases  me  most  is  that  it  con- 
tains all  the  late  results  of  research." 

Ski@im'§  Amsiilomy  ®f  Domsiltic  Aimimak 

Anatomy  of  Domestic  Animals.  By  Septimus  Sisson,  S.  B.,  V.  S., 
Professor  of  Comparative  Anatomy,  Ohio  State  University.  Octavo 
of  930 pages,  72s  illustrations.  Cloth,  $7.50  net.  New  {2d)  Edition. 
September,  1914. 

Here  is  a  work  of  the  greatest  usefulness  in  the  study  and  pursuit  of 
the  veterinary  sciences.  This  is  a  clear  and  concise  statement  of  the 
structure  of  the  principal  domesticated  animals — an  exhaustive  gross 
anatomy  of  the  horse,  ox,  pig,  and  dog,  including  the  splanchnology  of 
the  sheep,  presented  in  a  form  never  before  approached  for  practical 
usefulness. 

Prof.  E.  D.  Harris,  North  Dakota  Agricultural  College:  "  It  is  the  best 
of  its  kind  in  the  English  language.     It  is  quite  free  from  errors." 

Skairp'i    V^itdirmaFy  OpklLkalm©I[@gy 

ophthalmology  for  Veterinarians.  By  Walter  N.  Sharp,  M.  D., 
Professor  of  Ophthalmology,  Indiana  \eterinary  College.  i2mo 
of  210  pages,  illustrated.     Cloth,  $2.00  net.  April,  IQ13. 

This  new  work  covers  a  much  neglected  but  important  field  of  veter- 
inary practice.  Dr.  Sharp  has  presented  his  subject  in  a  concise,  crisp 
way,  so  that  you  can  pick  up  his  book  and  get  to  "  the  point  "  quickly. 
He  first  gives  you  the  anatomy  of  the  eye,  then  examination,  the  various 
diseases,  including  injuries,  parasites,  errors  of  refraction. 
Dr.  George  H.  Glover,  Agricultural  Experiment  Station,  Fort  Collins: 
''  It  is  the  best  book  on  the  subject  on  the  market." 


lo  Saunders'  College  Text-Books 

The  Horse  in  Health  ani  Disease.  By  Frederick  B.  Hadley, 
D.  V.  M.,  Associate  Professor  of  Veterinary  Science,  Univetsity 
of  Wisconsin.     i2mo  of  260  pages,  illustrated.     Cloth,  $1.50  net. 

Publishei  August,  IQ15. 

This  new  work  correlates  the  structure  and  function  of  each  organ  of 
the  body,  and  shows  how  the  hidden  parts  are  related  to  the  form, 
movements,  and  utility  of  the  animal.  Then,  in  another  part,  you  get 
a  concise  discussion  of  the  causes,  methods  of  prevention,  and  effects 
of  disease.  The  book  is  designed  especially  as  an  introductory  text  to 
the  study  of  veterinary  science  in  agricultural  schools  and  colleges. 


Kii"Mpp^i  PoMkiry  CMM^ird 

Poultry  Culture,  Sanitation,  ani  Hygiene.  By  B.  F.  Kaupp,  M.  S., 
D.  V.  M.,  Poultry  Investigator  and  Pathologist,  North  Carolina 
Experiment  Station  i2mo  of  417  pages,  with  iq7  illustrations. 
Cloth,  $2.00  net.  Published  September.  IQ15. 

This  work  gives  you  the  breeds  and  varieties  of  poultry,  hygiene  and 
sanitation,  ventilation,  poultry-house  construction,  equipment,  ridding 
stock  of  vermin,  internal  parasites,  and  other  diseases.  You  get  the 
gross  anatomy  and  functions  of  the  digestive  organs,  food-stuffs,  com- 
pounding rations,  fattening,  dressing,  packing,  selling,  care  of  eggs, 
handling  feathers,  value  of  droppings  as  fertilizer,  caponizing,  etc.,  etc. 


Lyiffick^s  D5§(iii§(i§  ©IF  Swma 

Diseases  of  Swine.  With  Particular  Reference  to  Hog-Cholera. 
By  Charles  F.  Lynch,  M.  D.,  D.  V.  S.,  Terre  Haute  Veterinary 
College.  With  a  chapter  on  Castration  and  Spaying,  by  George 
R.  White,  M.  D.,  D.  V.  S.,  Tennessee.  Octavo  of  741  pages, 
illustrated.     Cloth,  $5.00  net.  Published  November,  IQ14. 

You  get  first  some  80  pages  on  the  various  breeds  of  hogs,  with  vahi- 
ahle  points  in  judging  swine.  Then  comes  an  extremely  important 
monograph  of  over  400  pages  on  hog-cholera,  giving  the  history,  causes, 
pathology,  types,  and  treatment.  Then,  in  addition,  you  get  complete 
chapters  on  all  other  diseases  of  swine. 


Saunders'   College  Text-Books  1 1 


Live  Slock  on  the  Farm.  By  Wiilliam  Dietrich,  Ph.D.,  Depart- 
ment of  Agriculture,  University  of  Minnesota.  i2nio  of  275  pages, 
illustrated.  Ready  August,  igiy. 

This  work  takes  up  the  entire  question  of  the  care  of  all  kinds  of  live 
stock — horses,  the  dairy  cow,  beef  cattle,  sheep,  swine,  poultry  of  all 
kinds.  There  is  a  large  section  on  feeding;  another  on  breeding  for 
special  uses,  castration,  tuberculin  test,  cholera  vaccination,  etc.,  etc. 
It  is  a  clear  presentation  of  economic  live  stock  raising,  based  on  sound 
scientific  principles.  You  are  told  how  to  select,  breed,  feed,  use,  and 
sell  animals.  Scientific  feeding  is  gone  into  very  thoroughlj',  and  exact 
quantities,  costs,  and  kinds  of  food  are  detailed. 

Ka^pp^s  Aimatoimiiy  ©f  tKm  F©wl 

Anatomy  of  the  Fowl.  By  B.  F.  Kaupp,  M.  S.,  D.  V.  M.,  Poultry 
Investigator  and  Pathologist,  North  Carolina  Experiment  Station. 
i2mo  of  400  pages,  illustrated.  Ready  .August,  IQ17. 

Here  j'ou  get  a  systematic  text -book,  based  on  laboratory  studies.  The 
work  takes  up  osteology,  the  articulations,  the  musculature,  the  viscera, 
the  veins,  arteries  and  lymphatics,  neurology,  the  special  senses.  There 
is  a  chapter  on  embryology  and  on  the  methods  of  preparing  specimens. 
Professor  Kaupp's  long  experience  and  special  training  in  this  field  fit 
him  most  admirably  to  write  an  instructive  work  such  as  this  is.  It 
adequately  fills  the  need  for  an  advanced  work  in  the  study  of  poultry 
husbandry  now  being  carried  on  so  extensively. 

Hygiene.  By  D.  H.  Bergey,  M.  D.,  Assistant  Professor  of  Bac- 
teriology, University  of  Pennsyh'ania.  Octavo  of  529  pages,  illus- 
trated.    Cloth,  $3.00  net.  Fifth  Edition — September,  iQt4. 

Dr.  Bergey  gives  first  place  to  ventilation,  water-supply,  sewage,  indus- 
trial and  school  hygiene,  etc.  His  long  experience  in  teaching  this  sub- 
ject has  made  him  familiar  with  teaching  needs.  He  gives  you  not  onh- 
the  latest  investigations  in  the  laboratory,  but  also  practical  advances 
made  in  administration  and  application  of  sanitary  measures. 

J.  N.  Hurty,  M.  D.,  Indiana  University:  "  It  is  one  of  the  best  books 
with  which  I  am  acquainted." 


12  Saunders'  College  Text-Books 


Immediate  Care  of  the  Injured.  By  Albert  S.  Morrow,  M.  D., 
Adjunct  Professor  of  Surgery,  New  York  Polyclinic.  360  pages, 
242  illus      Cloth,  $2.50  net.  Second  Edition — March,  igi2. 

Dr.  Morrow's  book  tells  you  just  what  to  do  in  any  emergency,  and  it 
is  illustrated  in  such  a  practical  way  taat  the  idea  is  caught  at  once. 
There  is  no  book  better  adapted  to  first-aid  class  work. 

Health:  "Here  is  a  book  that  should  find  a  place  in  every  workshop 
and  factory  and  should  be  made  a  text-book  in  our  schools." 


^merncami  iiiiiiM§ttirat£@(dl  lUmU©: 

American  Illustrated  Rledical  Dictionary.  By  W.A.Newman 
DoRLAND,  M.  D.,  Member  of  Committee  on  Nomenclature  and 
Classification  of  Diseases,  American  Medical  Association.  Octava 
of  1137  pages,  324  illustrations,  up  in  colors.  Flexible  leather, 
$4.50  net;  indexed,  $5.00  net.  Eighth  Edition — August,  IQ15. 

If  you  want  an  unabridged  medical  dictionary,  this  is  the  one  you 
want.  It  is  down  to  the  minute;  its  definitions  are  concise,  yet  accu- 
rate and  clear;  it  is  extremely  easy  to  consult;  it  defines  all  the  newest 
terms  in  medicine  and  the  allied  subjects;  it  is  profusely  illustrated. 
John  B.  Murphy,  M.  D.,  Northwestern  University:  "  It  is  unquestion- 
ably the  best  lexicon  on  medical  topics  in  the  English  language,  and 
with  all  that,  it  is  so  compact  for  ready  reference." 

American  Pocket  Medical  Dictionary.  Edited  by  W.  A.  New- 
man Borland,  M.  D.  693  'pages.  Flexible  leather,  $1.25  net; 
thumb  index,  $1.50  net.  Ninth  Edition— April,  1915. 

A  dictionary  must  be  full  enough  to  give  the  student  the  information 
he  seeks,  clearly  and  simply,  yet  it  must  not  confuse  him  with  detail. 
The  editor  has  kept  this  in  mind  in  compiling  this  Pocket  Dictionary. 

I.  V.  S.  Stanislaus,  M.  D.,  Medico-Chirurgical  College:  "We  have 
been  strongly  recommending  this  little  book  as  being  the  very  best." 

DESCRIPTIVE   CIRCULARS   OF  ALL   BOOKS    SENT   FREE 


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